Post by thread:[OT]: Battery power circuit

Anyone know where I can find general information concerning battery powering a PIC based circuit? I'm currently running off a 12V 1A wall wart, through a small 7805 circuit. I've hooked up a 9V battery in place of the wall wart, seemed to work, but I'm guessing there's a much better way. I don't know how much current I'll actually need since I'm still learning/designing. I know this is a vague, newbie question, I just looking for considerations for using batteries and support power circuitry that wastes little but still works with damaging my 16F84. Any pointers would be appreciated. Thanks, Kevin -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On the test bench I frequently use a pack with 4 nicads. It is very close to 5 volts, then I don't need a regulator. For a production device you need to do something more complicated. Cheers, Bob On Wed, 14 Mar 2001, Kevin Olalde wrote: {Quote hidden}> Anyone know where I can find general information concerning battery > powering a PIC based circuit? > > I'm currently running off a 12V 1A wall wart, through a small 7805 > circuit. I've hooked up a 9V battery in place of the wall wart, seemed > to work, but I'm guessing there's a much better way. I don't know how > much current I'll actually need since I'm still learning/designing. > > I know this is a vague, newbie question, I just looking for > considerations for using batteries and support power circuitry that > wastes little but still works with damaging my 16F84. > > Any pointers would be appreciated. > > Thanks, > > Kevin > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 06:08 PM 3/14/01 -0500, Kevin Olalde wrote: >Anyone know where I can find general information concerning battery >powering a PIC based circuit? > >I'm currently running off a 12V 1A wall wart, through a small 7805 circuit. Not a bad start, but maybe worse than it seems (how's that for encouragement) 12V wall warts come in many flavours. AC, rectified but unfiltered (the commonest), barely filtered, well filtered, regulated, and switchers. You want at least a rectified wall wart, plus a decent sized filter cap. 1000uF/A is typical. The main thing is that under load, low line etc, the min output voltage can't be less than about 7V into the reg. Also, you don't want the voltage any higher than you need, because the reg will dissipate all of the extra power as heat. Ex: 12V in at 1A, 5V out at 1A, reg dissipates 7W, project dissipates 5W. I've used 12V gell cells with a wall-wart charger as a good compromise supply. You actually run on the batteries, and they are better at supplying pulse current. 9V transistor batteries are going to make you poor real fast. -- Dave's Engineering Page: http://www.dvanhorn.org Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Well, start with Microchip's website, specifically the appnotes, specifically AN606. Then troll the archives for low-dropout regulators. The 78xx and 78Lxx series regulators are terrible for battery-operated equipment, but fine with a wallwart. There are lots of LDOs, they work great and are simple to use: for example, desolder 78L05, solder in LDO. More complex, but interesting, are switching regulators that boost 1.5 volts to 3 volts, or 3 volts to 5 volts, thus allowing AA or AAA batteries to be used. But be careful if you have circutry that is sensitive to noise, for example, an ADC you paid >$15 for. the racket the step-up regulators make may limit the resolution of a nice ADC to the resolution you could get with a wet string. alice {Quote hidden}> Anyone know where I can find general information concerning battery > powering a PIC based circuit? > > I'm currently running off a 12V 1A wall wart, through a small 7805 > circuit. I've hooked up a 9V battery in place of the wall wart, seemed > to work, but I'm guessing there's a much better way. I don't know how > much current I'll actually need since I'm still learning/designing. > > I know this is a vague, newbie question, I just looking for > considerations for using batteries and support power circuitry that > wastes little but still works with damaging my 16F84. > > Any pointers would be appreciated. > > Thanks, > > Kevin > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Kevin Olalde wrote: >> >>I'm currently running off a 12V 1A wall wart, through a small 7805 circuit. >>circuit. I've hooked up a 9V battery in place of the wall wart, seemed >>to work, but I'm guessing there's a much better way. I don't know how >>much current I'll actually need since I'm still learning/designing. > >>I know this is a vague, newbie question, I just looking for >>considerations for using batteries and support power circuitry that >>wastes little but still works with damaging my 16F84. Kevin, If you are considering running off 9v battery power some of the time, then you should look into ways to reduce current draw in the circuit. Those batteries only have about 500 mAH of juice [IIRC]. Try LDO/low-quiescent current regulators as Alice mentioned, using a crystal no faster than absolutely necessary for the app, going into sleep mode between ops, CMOS for opamps and other circuitry. Changing to a more efficient v.reg is the first step. Also, regarding the wall wart, you can probably get by with a much smaller variety. Be aware that a 12v, 1A W/W probably puts out 15-17v unloaded, and it is unlikely you will need 1A for a while anyway. Even a 6vdc, 200-300 mA W/W will easily run a device eventually slated for battery ops. For a very low draw datalogger, I have even used 2 3v lithium batteries in series to drive an LDO v.reg. The output of a standard DC W/W is usually not regulated, but should work ok with a v.reg and 10-22 uF electrolytic caps for filtering. Better to steer clear of AC output W/Ws, as these will require more complicated power circuitry. - Dan Michaels http://www.oricomtech.com ================== -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Bob Blick wrote: >On the test bench I frequently use a pack with 4 nicads. It is very close >to 5 volts, then I don't need a regulator. > Dave Van Horn wrote: >I've used 12V gell cells with a wall-wart charger as a good compromise supply. >You actually run on the batteries, and they are better at supplying pulse >current. Good, we have 2 battery jockeys here today. This question just came up yesterday :). What happens when you operate your PIC off batteries, and the batteries run down so much that the v.reg output drops down below the normal operating range? I made some measurements on this [again, yesterday], and discovered: Things tend to function down to a point. The output of the v.reg just falls off as the voltage in to it falls. Current draw in the ckt continues to drop - the v.reg doesn't seem to go berserk or stall/etc. More importantly, if you allow Vdd to the PIC to drop below the lower spec limit, I assume the PIC will simply stop running. However, I wonder whether it will damage the PIC to leave below spec Vdd on it for a "long" period of time. Anybody know about this? - dan michaels http://www.oricomtech.com ================== -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> >What happens when you operate your PIC off batteries, and the batteries >run down so much that the v.reg output drops down below the normal >operating range? Short version: Wierdness. Don't go there. You don't even want to run it low enough that the reg stops regulating if you can avoid it. Definitely, you should have /MCLR asserted before VCC drops out of spec. >More importantly, if you allow Vdd to the PIC to drop below the lower >spec limit, I assume the PIC will simply stop running. However, I >wonder whether it will damage the PIC to leave below spec Vdd on >it for a "long" period of time. Nothing in the micro will be damaged, but it may erase internal EEPROM, or the outputs may go into states that cause problems in other parts of the circuit. -- Dave's Engineering Page: http://www.dvanhorn.org Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Great, thanks all, this will get me started. I think a switching regulator may be what I need. I'd rather not have to put 4 AAAs in the project just to use a LDO to get back to 5V (too big/heavy anyway, I'm going for small). Are all switching regulators so expensive (>$5 range)? Thanks, Kevin Alice Campbell wrote: {Quote hidden}> > Well, start with Microchip's website, specifically the > appnotes, specifically AN606. > > Then troll the archives for low-dropout regulators. > > The 78xx and 78Lxx series regulators are terrible for > battery-operated equipment, but fine with a wallwart. > > There are lots of LDOs, they work great and are simple to > use: for example, desolder 78L05, solder in LDO. > > More complex, but interesting, are switching regulators that > boost 1.5 volts to 3 volts, or 3 volts to 5 volts, thus > allowing AA or AAA batteries to be used. But be careful if > you have circutry that is sensitive to noise, for example, an > ADC you paid >$15 for. the racket the step-up regulators > make may limit the resolution of a nice ADC to the resolution > you could get with a wet string. > > alice > > > Anyone know where I can find general information concerning battery > > powering a PIC based circuit? > > > > I'm currently running off a 12V 1A wall wart, through a small 7805 > > circuit. I've hooked up a 9V battery in place of the wall wart, seemed > > to work, but I'm guessing there's a much better way. I don't know how > > much current I'll actually need since I'm still learning/designing. > > > > I know this is a vague, newbie question, I just looking for > > considerations for using batteries and support power circuitry that > > wastes little but still works with damaging my 16F84. > > > > Any pointers would be appreciated. > > > > Thanks, > > > > Kevin > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 11:56 PM 3/14/01 -0500, Kevin Olalde wrote: >Great, thanks all, this will get me started. I think a switching >regulator may be what I need. I'd rather not have to put 4 AAAs in the >project just to use a LDO to get back to 5V (too big/heavy anyway, I'm >going for small). Are all switching regulators so expensive (>$5 >range)? In small quantities they aren't cheap. In volume, you buy your inductors in china for pennies, and you might not even use an SMPS chip, just a couple of transistors. Low current boost regs are a great way to get started with switchers. Well behaved, and if anything goes wrong, minimal smoke. Beware the charlatan with the charge pump capacitor converter though. The efficiency is terrible. -- Dave's Engineering Page: http://www.dvanhorn.org Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Just curious - what's wrong with three alkaline AA's? Planning on usig lots of LEDs or servos? I get a month or so out of a set. On Wed, 14 Mar 2001, Kevin Olalde wrote: {Quote hidden}> Great, thanks all, this will get me started. I think a switching > regulator may be what I need. I'd rather not have to put 4 AAAs in the > project just to use a LDO to get back to 5V (too big/heavy anyway, I'm > going for small). Are all switching regulators so expensive (>$5 > range)? > > Thanks, > > Kevin > > Alice Campbell wrote: > > > > Well, start with Microchip's website, specifically the > > appnotes, specifically AN606. > > > > Then troll the archives for low-dropout regulators. > > > > The 78xx and 78Lxx series regulators are terrible for > > battery-operated equipment, but fine with a wallwart. > > > > There are lots of LDOs, they work great and are simple to > > use: for example, desolder 78L05, solder in LDO. > > > > More complex, but interesting, are switching regulators that > > boost 1.5 volts to 3 volts, or 3 volts to 5 volts, thus > > allowing AA or AAA batteries to be used. But be careful if > > you have circutry that is sensitive to noise, for example, an > > ADC you paid >$15 for. the racket the step-up regulators > > make may limit the resolution of a nice ADC to the resolution > > you could get with a wet string. > > > > alice > > > > > Anyone know where I can find general information concerning battery > > > powering a PIC based circuit? > > > > > > I'm currently running off a 12V 1A wall wart, through a small 7805 > > > circuit. I've hooked up a 9V battery in place of the wall wart, seemed > > > to work, but I'm guessing there's a much better way. I don't know how > > > much current I'll actually need since I'm still learning/designing. > > > > > > I know this is a vague, newbie question, I just looking for > > > considerations for using batteries and support power circuitry that > > > wastes little but still works with damaging my 16F84. > > > > > > Any pointers would be appreciated. > > > > > > Thanks, > > > > > > Kevin > > > > > > -- > > > http://www.piclist.com hint: The list server can filter out subtopics > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > > > > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > --- The most exciting phrase to hear in science, the one that heralds new discoveries, is not "Eureka!" (I found it!) but "That's funny ..." -- Isaac Asimov -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Beware the charlatan with the charge pump capacitor converter though. The efficiency is terrible. Even compared to a linear regulator? Most of the "regulated" charge pump capacitors double the battery voltage and then run that through a LDO linear regulator. IIRC, the doubler efficiency is about 85%, and the linear regulator efficiency is "typical and as required by physics." On the flip side, 2AA cells contain quite a bit more energy, for a lower price, than a 9V alkaline, so if you're specifically after increased battery life, you may still win... (and you'll do significantly better if you can do without the regulator, somehow letting the voltage drop from Vccmax to Vccmin...) There's an interesting power supply circuit for the (ultra-low power) MSP430 on TI's web site. It uses four transistors to drive a capacitive voltage doubler to run the processor (which requires 1.8 to 3.6V) from a single 1.5V battery. It ought to work with higher input voltages as well. http://www.ti.com/sc/docs/psheets/abstract/apps/slaa105.htm BillW -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 10:21 PM 3/14/01 -0800, William Chops Westfield wrote: > Beware the charlatan with the charge pump capacitor converter though. > The efficiency is terrible. > >Even compared to a linear regulator? As a switcher. Linears don't do voltage boost. Except for size, it's pretty hard to beat a low R coil, schottky diode, and low RDSon mosfet. >Most of the "regulated" charge pump capacitors double the battery >voltage and then run that through a LDO linear regulator. IIRC, the >doubler efficiency is about 85%, and the linear regulator efficiency is >"typical and as required by physics." The problem is in the switches. The charge pump requires relatively high currents through the switches, which are never very good switches. > On the flip side, 2AA cells >contain quite a bit more energy, for a lower price, than a 9V alkaline, >so if you're specifically after increased battery life, you may still >win... (and you'll do significantly better if you can do without the >regulator, somehow letting the voltage drop from Vccmax to Vccmin...) AA cells are about the best bang for the buck. -- Dave's Engineering Page: http://www.dvanhorn.org Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

If you are using a low power circuit, look at the MAX619. This is what I use on the AC-22 Performance Meter, that takes about 40mA and will operate for about 30-40 hours from a pair of AA Zinc Chloride batteries, this is OK for upto about 50mA with input voltages down to about 2V. Martin {Quote hidden}> Great, thanks all, this will get me started. I think a switching > regulator may be what I need. I'd rather not have to put 4 AAAs in the > project just to use a LDO to get back to 5V (too big/heavy anyway, I'm > going for small). Are all switching regulators so expensive (>$5 > range)? > > Thanks, > > Kevin > > Alice Campbell wrote: > > > > Well, start with Microchip's website, specifically the > > appnotes, specifically AN606. > > > > Then troll the archives for low-dropout regulators. > > > > The 78xx and 78Lxx series regulators are terrible for > > battery-operated equipment, but fine with a wallwart. > > > > There are lots of LDOs, they work great and are simple to > > use: for example, desolder 78L05, solder in LDO. > > > > More complex, but interesting, are switching regulators that > > boost 1.5 volts to 3 volts, or 3 volts to 5 volts, thus > > allowing AA or AAA batteries to be used. But be careful if > > you have circutry that is sensitive to noise, for example, an > > ADC you paid >$15 for. the racket the step-up regulators > > make may limit the resolution of a nice ADC to the resolution > > you could get with a wet string. > > > > alice > > > > > Anyone know where I can find general information concerning battery > > > powering a PIC based circuit? > > > > > > I'm currently running off a 12V 1A wall wart, through a small 7805 > > > circuit. I've hooked up a 9V battery in place of the wall wart, seemed > > > to work, but I'm guessing there's a much better way. I don't know how > > > much current I'll actually need since I'm still learning/designing. > > > > > > I know this is a vague, newbie question, I just looking for > > > considerations for using batteries and support power circuitry that > > > wastes little but still works with damaging my 16F84. > > > > > > Any pointers would be appreciated. > > > > > > Thanks, > > > > > > Kevin > > > > > > -- > > > http://www.piclist.com hint: The list server can filter out subtopics > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > > > > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

One of the compnents in the circuit requires 4.5-5.5V. Three AA's would get me to 4.5, but I assumed it'd drop off too quickly and I'd be below spec. Part of my concern was how to avoid under powering items (which seems to be getting discussed). Can someone eleborate on how to "have /MCLR asserted before VCC drops out of spec"? Thanks. Kevin Dale Botkin wrote: {Quote hidden}> > Just curious - what's wrong with three alkaline AA's? Planning on usig > lots of LEDs or servos? I get a month or so out of a set. > > On Wed, 14 Mar 2001, Kevin Olalde wrote: > > > Great, thanks all, this will get me started. I think a switching > > regulator may be what I need. I'd rather not have to put 4 AAAs in the > > project just to use a LDO to get back to 5V (too big/heavy anyway, I'm > > going for small). Are all switching regulators so expensive (>$5 > > range)? > > > > Thanks, > > > > Kevin > > > > Alice Campbell wrote: > > > > > > Well, start with Microchip's website, specifically the > > > appnotes, specifically AN606. > > > > > > Then troll the archives for low-dropout regulators. > > > > > > The 78xx and 78Lxx series regulators are terrible for > > > battery-operated equipment, but fine with a wallwart. > > > > > > There are lots of LDOs, they work great and are simple to > > > use: for example, desolder 78L05, solder in LDO. > > > > > > More complex, but interesting, are switching regulators that > > > boost 1.5 volts to 3 volts, or 3 volts to 5 volts, thus > > > allowing AA or AAA batteries to be used. But be careful if > > > you have circutry that is sensitive to noise, for example, an > > > ADC you paid >$15 for. the racket the step-up regulators > > > make may limit the resolution of a nice ADC to the resolution > > > you could get with a wet string. > > > > > > alice > > > > > > > Anyone know where I can find general information concerning battery > > > > powering a PIC based circuit? > > > > > > > > I'm currently running off a 12V 1A wall wart, through a small 7805 > > > > circuit. I've hooked up a 9V battery in place of the wall wart, seemed > > > > to work, but I'm guessing there's a much better way. I don't know how > > > > much current I'll actually need since I'm still learning/designing. > > > > > > > > I know this is a vague, newbie question, I just looking for > > > > considerations for using batteries and support power circuitry that > > > > wastes little but still works with damaging my 16F84. > > > > > > > > Any pointers would be appreciated. > > > > > > > > Thanks, > > > > > > > > Kevin > > > > > > > > -- > > > > http://www.piclist.com hint: The list server can filter out subtopics > > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > > > > > > > > > > > > -- > > > http://www.piclist.com hint: The list server can filter out subtopics > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > --- > The most exciting phrase to hear in science, the one that heralds new > discoveries, is not "Eureka!" (I found it!) but "That's funny ..." > -- Isaac Asimov > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Dan Michaels wrote: > If you are considering running off 9v battery power some of the time, > then you should look into ways to reduce current draw in the circuit. > Those batteries only have about 500 mAH of juice [IIRC]. Yep. I was just testing with a 9V, but want to run off something smaller eventually. > Try LDO/low-quiescent current regulators as Alice mentioned, using a > crystal no faster than absolutely necessary for the app, I'm using 4MHz resonator. Part of the application will be sending/receiving serial data over RF links, I'd like to get 9600 buad out of it, so I'm guessing on my 16F84A-20 I won't want to go to a much slower crystal. (yes?) > going into > sleep mode between ops, CMOS for opamps and other circuitry. I definately like this path too. > Changing to a more efficient v.reg is the first step. Also, regarding > the wall wart, you can probably get by with a much smaller variety. > Be aware that a 12v, 1A W/W probably puts out 15-17v unloaded, and > it is unlikely you will need 1A for a while anyway. I should have been more clear. It's actually a rated for DC 9V 1A, I'm driving very little, so I was assuming it was putting out 12V.......I just measured it, about 12.8V before the regulator. > Even a 6vdc, > 200-300 mA W/W will easily run a device eventually slated for > battery ops. For a very low draw datalogger, I have even used 2 3v > lithium batteries in series to drive an LDO v.reg. > > The output of a standard DC W/W is usually not regulated, but should > work ok with a v.reg and 10-22 uF electrolytic caps for filtering. > Better to steer clear of AC output W/Ws, as these will require more > complicated power circuitry. Yes, great advice. Lucikly for me I'm following some samples that I got for Peter Anderson's BS2 starter kit. 47uF caps electrolytic caps before and after the regulator and a diode across the 7805 for reverse voltage protection. So the WW and power supply is intended to be useful for small 12V motor experiments too. If I'm reading things correctly (which is a pretty big IF) the PIC will draw less than 2mA (unless in sleep mode). The RF transmitter's datasheet (TWS-434) says it has a peek current rating of 9mA. I'm going to keep away from things like LED/LCDs. The received data (over a RWS-434) will be serially sent to a pda (have to lookup the current draw there). The pda will also provide input to the PIC which it will send through the transmitter. I'm not sure of the receiver's current draw, I'm guessing it'd be less than that of the transmitter (although I don't know why I'd guess that, just sounds right). Thanks for all the input, great group! Kevin -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Kevin Olalde wrote: > >> Try LDO/low-quiescent current regulators as Alice mentioned, using a >> crystal no faster than absolutely necessary for the app, > >I'm using 4MHz resonator. Part of the application will be >sending/receiving serial data over RF links, I'd like to get 9600 buad >out of it, so I'm guessing on my 16F84A-20 I won't want to go to a much >slower crystal. (yes?) > Actually, with finely-tuned code, you should be able to get upwards to 115,200 baud when using an xtal in the 4Mhz range. This would be where the instructions that sample the RxD line and build up received bytes exactly equal the time to process one character, with no additional delays inserted in the code. =========== > >Yes, great advice. Lucikly for me I'm following some samples that I got >for Peter Anderson's BS2 starter kit. 47uF caps electrolytic caps >before and after the regulator and a diode across the 7805 for reverse >voltage protection. So the WW and power supply is intended to be useful >for small 12V motor experiments too. > IIRC, the reverse diode across the 7805 doesn't actually provide for reverse voltage protection, but prevents the cap on the output of the v.reg chip from discharging back into the chip when power is removed. You would actually need a diode in series in the line from the battery to protect from reverse voltages. ============ {Quote hidden}>If I'm reading things correctly (which is a pretty big IF) the PIC will >draw less than 2mA (unless in sleep mode). The RF transmitter's >datasheet (TWS-434) says it has a peek current rating of 9mA. I'm going >to keep away from things like LED/LCDs. The received data (over a >RWS-434) will be serially sent to a pda (have to lookup the current draw >there). The pda will also provide input to the PIC which it will send >through the transmitter. I'm not sure of the receiver's current draw, >I'm guessing it'd be less than that of the transmitter (although I don't >know why I'd guess that, just sounds right). > Also, if interfacing with a PDA, you will have to check on relevant voltage levels - PDA<->RWS-434 and possibly also PDA<->PIC. If you are going to use RS-232 comms, then your PIC needs a level translator like MAX232 chip or something similar. Unfortunately the MAX's draw several mA continuously, so they will also drain your battery. You might look at some of the BJT RS-232 circuits, such as that used on the Basic Stamps, which draw zero quiescent current. Can be found somewhere on piclist/techref, and I also have an appnote about this: AN-ECD02 - A Simple Inexpensive Network-Compatible RS-232 Interface http://www.oricomtech.com/appnotes.htm - dan michaels ============== -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> >IIRC, the reverse diode across the 7805 doesn't actually provide for >reverse voltage protection, but prevents the cap on the output of the >v.reg chip from discharging back into the chip when power is removed. >You would actually need a diode in series in the line from the >battery to protect from reverse voltages. >============ Almost right. Large caps on the output of the reg can destroy the reg, if the reg input is shorted to ground. The diode provides a safe place for that current to go. It's documented sporadically, but is true for all 78XX, 340T-XX and similar regs. -- Dave's Engineering Page: http://www.dvanhorn.org Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Ok, heres a booster ive been messing with, it delivers about 15mA in this incarnation. Im trying for about 20 mA and 4 ot 5 volts. in 2-3 V | | ----------------|---------| < | | > R1 ---K pnp < R2 < | \ > D1 | | \ o-->I-o-o---out ~4-5V |---o-------K npn | | | | | | | | | Z = C2 | -----------||--o-RR--K npn | | | | C1 R3 | | | |-------------------------------| | | | | vss vss vss R1=1M R2=220-450r R3=1K or more C1=0.1u C2=>50u Z=zener, your choice, 5.1 maybe D1=small diode maybe shottkey I would welcome improvements, this is my first attempt. alice Are all switching regulators so expensive (>$5 {Quote hidden}> >range)? > > In small quantities they aren't cheap. > In volume, you buy your inductors in china for pennies, and you might not > even use an SMPS chip, just a couple of transistors. > > Low current boost regs are a great way to get started with switchers. > Well behaved, and if anything goes wrong, minimal smoke. > > Beware the charlatan with the charge pump capacitor converter though. The > efficiency is terrible. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Kevin wrote: >One of the compnents in the circuit requires 4.5-5.5V. Three AA's would >get me to 4.5, but I assumed it'd drop off too quickly and I'd be below >spec. Part of my concern was how to avoid under powering items (which >seems to be getting discussed). > >Can someone eleborate on how to "have /MCLR asserted before VCC drops >out of spec"? Thanks. This means using a voltage supervisor of some sort. We use the Seiko S8054 series and Microchip MCP120 series in our designs all the time. It's a 3 pin device that pulls its output low when the supply drops below a certain level. This way, the PIC is kept in reset until the power is up to spec. This prevents the PIC from running when the voltage is too low and doing "weird" stuff ! :-) Regards... -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Alice Campbell wrote: {Quote hidden}> > Ok, heres a booster ive been messing with, it delivers about > 15mA in this incarnation. Im trying for about 20 mA and 4 ot > 5 volts. > > in 2-3 V > | > | > ----------------|---------| > < | | > > R1 ---K pnp < R2 > < | \ > D1 > | | \ o-->I-o-o---out ~4-5V > |---o-------K npn | | | | > | | | | | Z = C2 > | -----------||--o-RR--K npn | | > | | C1 R3 | | | > |-------------------------------| | > | | | > vss vss vss > > R1=1M > R2=220-450r > R3=1K or more > C1=0.1u > C2=>50u > Z=zener, your choice, 5.1 maybe > D1=small diode maybe shottkey > > I would welcome improvements, this is my first attempt. > > alice Hi Alice, if your buck inductor is a toroid type, maybe you could wrap an extra few turns of wire and use this winding to give neg feedback. This lets you use only one transistor (cost savings) and also gives some simple regulation as the load affects the voltage on the feedback winding. I see these in Akai VCRs, they don't use an inductor but instead a tiny RF can type coil with two windings driven by a small 500mA transistor. One coil, one tran and a couple of caps. Cheap as it gets! :o) -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

>More importantly, if you allow Vdd to the PIC to drop below the lower >spec limit, I assume the PIC will simply stop running. However, I >wonder whether it will damage the PIC to leave below spec Vdd on >it for a "long" period of time. I have had PICs in battery powered devices running with the battery down to 2V and below. Sometimes they do not do what they are meant to do anymore. If this is important you can use the brownout protection circuit to cause a reset when the battery goes low. One interesting problem is that brownout circuits without a hysterezis or 'latching' will cause the circuit to operate intermittently for many thousands of times near the end of life. What happens is: Circuit works -> Battery droops slowly -> brownout trips -> circuit in reset -> battery not loaded, increases slowly -> brownout releases reset and circuit works some more etc. I found it important to find out how long these periods can be and to build an initial delay into my code that prevents it from doing anything at all for up to 10 times as long. This means a 1-3 sec delay after reset and before setting up any TRIS registers in my code. This is still not enough if you try to do something at each turn-on (like increment a counter stored in EEPROM or such). hope this helps, Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

>On the test bench I frequently use a pack with 4 nicads. It is very close >to 5 volts, then I don't need a regulator. But you need a fuse ;-). I also used NiCds for this until what waited to happen happened. Since then I use 4 cheap AA batteries ($1 for 4) in a holder for that. I wear them out using a bulb first, until the voltage drops some, then run the circuit through one or two 1N4007 diodes (each drops ~0.5V at that current). The weak batteries are relatively short circuit proof as opposed to the NiCds and I can change the voltage for testing by clipping a crocodile clamp after one or two diodes. Of course the benchtop PSU is much better for this unless all its outputs are already used up... Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body