Post by thread:Cheap Reset Circuit -- With slowly rising Vcc (Bat

Guys, I have a problem. My micro is running in a battery operated environment where the battery pack is a part of the product. When the battery is completely dead ie around 2.4V the micro has stopped and so has the resonator. We then begin to charge the battery. The volatge starts to rise, at 3.2V we want the micro to startup. Do I need to go for a full blown Reset Controller? Or is there a simpler (cheaper) method. TIA Scott.

dallas semi has a reset chip that resets at 3.3 vdc. nothing could be easier to use only 3 pins. i will also say that any time you want to make something cheaper the reliability goes down faster than the price. if you are making a million parts the price is important but if you are making a hundred parts the reliability is important. michael At 03:51 PM 8/20/97 -0700, you wrote: {Quote hidden}> Guys, > > I have a problem. My micro is running in a battery operated > environment where the battery pack is a part of the product. > > When the battery is completely dead ie around 2.4V the micro has > stopped and so has the resonator. We then begin to charge the battery. > > The volatge starts to rise, at 3.2V we want the micro to startup. > > Do I need to go for a full blown Reset Controller? Or is there a > simpler (cheaper) method. > > TIA > Scott. > >

Seems like the watchdog timer would take care of this situation. It would keep resetting the processor, which continues to die until it is finally brought back to life once the battery voltage is high enough. Am I missing something? Harold On Wed, 20 Aug 1997 15:51:46 -0700 Scott Walsh <spam_OUTScott.WALSHTakeThisOuTPLANTRONICS.COM> writes: {Quote hidden}> Guys, > > I have a problem. My micro is running in a battery operated > environment where the battery pack is a part of the product. > > When the battery is completely dead ie around 2.4V the micro has > stopped and so has the resonator. We then begin to charge the >battery. > > The volatge starts to rise, at 3.2V we want the micro to startup. > > Do I need to go for a full blown Reset Controller? Or is there a > simpler (cheaper) method. > > TIA > Scott. >

I know of two generic methods to solve the problem. One is a transistor and resistors or a zener as shown in the data sheet. This is the least expensive (from component cost point of view) method. The other is to use a power supply supervisor. Check out Maxim and Dallas. This is a more expensive solution (US$1 to US$2), but they have features that might be worth the cost: Low power, smaller footprint, more precise, and turn-on delay. I believe that you will find that you will need to handle reset in some way. I have a product that I am recalling because of this. Believe me, it's better to do it right the first time. The watchdog does _NOT_ work reliable after broun-out. I have no explaination for this, only experience with 16F84s. The 'F84s will wake up "sort of" working, and the watchdog will not do a proper reset. Ports wake up in a funny mode (not documented) and there is a good possibility that the EEPROM is corrupted. Regards, Jim At 03:51 PM 8/20/97 -0700, you wrote: {Quote hidden}> Guys, > > I have a problem. My micro is running in a battery operated > environment where the battery pack is a part of the product. > > When the battery is completely dead ie around 2.4V the micro has > stopped and so has the resonator. We then begin to charge the battery. > > The volatge starts to rise, at 3.2V we want the micro to startup. > > Do I need to go for a full blown Reset Controller? Or is there a > simpler (cheaper) method. > > TIA > Scott. > > Jim Ham, Porcine Associates (415)326-2669 fax(415)326-1071 "http://www.porcine.com"

On 20 Aug 97 at 20:57, Jim Ham wrote: > I know of two generic methods to solve the problem. One is a > transistor and resistors or a zener as shown in the data sheet. This > is the least expensive (from component cost point of view) method. > The other is to use a power supply supervisor. Check out Maxim and > Dallas. This is a more expensive solution (US$1 to US$2), but they > have features that might be worth the cost: Low power, smaller > footprint, more precise, and turn-on delay. I believe that you will > find that you will need to handle reset in some way. I have a > product that I am recalling because of this. Believe me, it's better > to do it right the first time. > > The watchdog does _NOT_ work reliable after broun-out. I have no > explaination for this, only experience with 16F84s. The 'F84s will > wake up "sort of" working, and the watchdog will not do a proper > reset. Ports wake up in a funny mode (not documented) and there is a > good possibility that the EEPROM is corrupted. Reset doesn't always seem to remedy some of the problems, either. How about a 'snap' action on the Vdd pin? (so any voltage below, say 4 volts give 0 v output, then turns on quickly at above 4 volts) MikeS <.....mikesmith_ozKILLspam@spam@relaymail.net> === For PICLIST help (including "unsubscribe" instructions), === send an e-mail containing the single phrase "help piclist" === to: listservKILLspammitvma.mit.edu

On Wed, 20 Aug 1997 20:57:30 -0700 Jim Ham <.....jimhamKILLspam.....PORCINE.COM> writes: >The watchdog does _NOT_ work reliable after broun-out. I have no >explaination for this, only experience with 16F84s. The 'F84s will >wake up >"sort of" working, and the watchdog will not do a proper reset. Ports >wake >up in a funny mode (not documented) and there is a good possibility >that >the EEPROM is corrupted. Wow! Major problem! I'd hoped that the watchdog timer would recover from ANYTHING once the power was back up to where the processor could function. In another couple products (one using a 68B02, the other using a PC motherboard), I built a watchdog timer out of a 74HC14 and several resistors, diodes, and capacitors. It generates a power-up reset and works as a watchdog, requiring a pulse to its input every now and then to prevent it from timing out. The input is AC coupled so if the system crashes during a reset it doesn't get stuck. As far as eeprom getting corrupted... that seems to be a way of life. In that 68B02 project, I used an MK48T02 "TimeKeeper RAM" (a neat part, by the way). It has a real time clock and a little under 2 Kbytes of battery backed static RAM. I added gating to the write strobe so the processor had to enable writing prior to doing a write. I'm sure it helps, but every now and then I get a call from a customer with corrupted set-up data. I haven't used a PIC with an eeprom in it, so I have no experience with its protection... Harold