Post by thread:] Design Challenge

>-----Original Message----- >From: Russell McMahon [spam_OUTapptechTakeThisOuTPARADISE.NET.NZ] >Sent: 09 July 2004 10:37 >To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU >Subject: [EE:] Design Challenge - Lowest cost PWM >A 555 MAY be able to do most of this by itself. Prove it :-) > Many years ago I designed a motor speed controller using 556, one timer configured as an fixed fequency astable, triggering the other timer configured as a monostable with variable pulse width (using the control voltage input). This drove a car starter motor via a bank of about 20 2N3055's (and a high power driver stage, suitable MOSFETS were very expensive at the time, and 2N3055's were dirt cheap on the surplus market). Linearity won't be good with the standard monostable due to the capacitor being charged by a resistor, and compared to the reference. Replacing the resistor with a simple constant current source (maybe a jfet or constant current "diode") should improve this considerably. Getting 0% and 100% may be trickier! You might also look at the retriggerable monostables available in the cheap logic families, perhaps using a simple voltage controlled current source to charge the timing cap. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu

>>A 555 MAY be able to do most of this by itself. Prove it :-) > >Many years ago I designed a motor speed controller using 556, one timer >configured as an fixed fequency astable, triggering the other timer >configured as a monostable with variable pulse width (using the control >voltage input). Russell I worked at the DSIR in Gracefield, Wellington, for a couple of years, and one of the projects there was a 5V 10A switch mode supply (primarily to get experience with mains switchers) and it was done with a couple of 555's exactly like this. We did it back in the late 1970's. -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

Would a PIC12F675 using internal osc with code to control the PWM and AD's, with a linear or log pot as input, or with the PIC using it's A/D pin as input. The PIC code would be minimal, and certainly offset if the volume produced is high. Would that work? _____ Lindy > Subject: [EE:] Design Challenge - Lowest cost PWM > > [EE:] Design Challenge - Lowest cost PWM > --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.699 / Virus Database: 456 - Release Date: 6/4/2004 -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

> Would a PIC12F675 using internal osc with code to control the PWM and AD's, with a linear or log pot as input, or with the PIC using it's A/D pin as input. The PIC code would be minimal, and certainly offset if the volume produced is high. Would that work? > No hardware PWM I think. And cost is rather high compared with alternatives. Using Digikey as a guide (there MAY be cheaper but DK is easy to get comparison prices from). 12F675 is about $US1.35/1000s The tiny11 (also no hardware PWM) is $0.25 or less in that quantity! The question as to suitability of low frequency PWM is the only issue. _____________________________ > ATTiny13 would seem a good fit - internal RC osc, on-chip ADC, internal RC at up to 9.6MHZ you could get about 0.1uS PWM resolution in software, so about 0.2% resolution at 20KHz > A nice processor, but again, price is too high. About $US0.75/1000s And still no hardware PWM AFAIK. My PWM spec of at least 6 bits of resolution at 20 Khz means a PWM bit changes at 1/(20,000 x 2^16) = 0.78 uS At 20 Mhz you probably get about 15 MIPS (even though Atmel say 20 MIPS at 20 Mhz. If this sat in a tight loop doing nothing but PWm you would probably make it. 15MIPs * .78uS = ~ 12 instructions per PWM bit! Not really enough to run interupts. Reading an A2D in there would get tough. I've little doubt that Scott D could coax out the magic needed, but it still costs more than the analogue solution and does the PWM and nothing else. ______________________ Someone offlist suggested the Philips LPC901 8051 variant at under $US1 - and it has got hardware PWM. No A2D. Sigma Delta would work. ________________________ At present the tiny15 at about $US1.20/1000's with A2Ds and hadware PWM is attractive I have a solutuion working with ease with a tiny26 at $US1.30/1000s. Big brother to the 15 at about $US0.10 more. _____________ The HIP 4080 addresses the FET driving aspect but is dearish compared to other laternatives and doesn't seem to address the analog to PWM aspect (maybe I missed something there). ____________ I'm going to have to try a 4060 version "just to see". And read the LPC901 spec sheet more closely http://www.acqura.com/datasheets.asp?ID=499 RM -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

On Sat, 10 Jul 2004 01:04:22 +1200, you wrote: {Quote hidden}>> Would a PIC12F675 using internal osc with code to control the PWM and >AD's, with a linear or log pot as input, or with the PIC using it's A/D pin >as input. The PIC code would be minimal, and certainly offset if the volume >produced is high. >Would that work? >> > >No hardware PWM I think. And cost is rather high compared with alternatives. >Using Digikey as a guide (there MAY be cheaper but DK is easy to get >comparison prices from). 12F675 is about $US1.35/1000s > >The tiny11 (also no hardware PWM) is $0.25 or less in that quantity! The >question as to suitability of low frequency PWM is the only issue. > >_____________________________ > >> ATTiny13 would seem a good fit - internal RC osc, on-chip ADC, internal >RC at up to 9.6MHZ >you could get about 0.1uS PWM resolution in software, so about 0.2% >resolution at 20KHz >> > >A nice processor, but again, price is too high. About $US0.75/1000s >And still no hardware PWM AFAIK. >My PWM spec of at least 6 bits of resolution at 20 Khz means a PWM bit >changes at 1/(20,000 x 2^16) = 0.78 uS >At 20 Mhz you probably get about 15 MIPS (even though Atmel say 20 MIPS at >20 Mhz. If this sat in a tight loop doing nothing but PWm you would probably >make it. 15MIPs * .78uS = ~ 12 instructions per PWM bit! Not really enough >to run interupts. Reading an A2D in there would get tough. I've little doubt >that Scott D could coax out the magic needed, but it still costs more than >the analogue solution and does the PWM and nothing else You can get one-cycle software PWM resolution on a PIC or AVR, using either a short jump table to trim the PWM period, or timer interrupts. e.g. addwf pc nop nop nop will give you a 2 to 5 cycle trim for W values of 3 to 0 Timer int would normally be the best way as you'd have plenty of foreground time to play with. Any trickiness dealing with the whole 0..100% range can be overcome, if necessary with more than one piece of code. -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu