Post by thread:[PIC]: EE challenge PIC && 12V battery

part 1 596 bytes content-type:text/plain; (decoded 7bit) Hello Roman, All I think i go the discrete approach because of components availability reasons. The use of a capacitor for the hold time is clever but i dont like it, because the PIC would die down slowly by discharge unless you take special action to avoid this. Meanwhile i found a solution around the diodes to decouple the button information from their switch on function. By connecting the buttons to the - potential its possible to decouple them with resistors only. The values of them needs to be well defined however. See my picture. Germain Morbe part 2 7068 bytes content-type:image/gif; (decode) part 3 131 bytes -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

GMorbe wrote: >Attachment Converted: C:\WIN31APP\EUDORA\ATTACH\PICTX.gif > I wonder that you might not have a minor problem with your ckt. The typical leakage current into PIC input pins is ~1uA, so 10M series Rs would seem to be too high. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Dan, you may be right, the values have to be well defined. The shown values are not tested yet, but are a rough calculation to start with. See the time stamp of my posting. Thank you, i will check it this morning. :) Germain Morbe -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

GMorbe wrote: > > Hello Roman, All > > I think i go the discrete approach because of components availability > reasons. > The use of a capacitor for the hold time is clever but i dont like it, > because the PIC would die down slowly by discharge unless you take special > action to avoid this. > Meanwhile i found a solution around the diodes to decouple the button > information from their switch on function. By connecting the buttons to > the - potential its possible to decouple them with resistors only. The > values of them needs to be well defined however. See my picture. > > Germain Morbe Hi Germain. I'm not sure I like the design. Your 12v battery voltage is permanently connected to the two PIC pins, which: 1. is way out of voltage spec!! 2. will drain battery into the PIC protection diodes. Why not replace the 10M with 1N4148 glass diodes, these are cheaper and smaller than resistors, and will solve the two problems... -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

{Quote hidden}> -----Original Message----- > From: Roman Black [SMTP:fastvidKILLspamEZY.NET.AU] > Sent: Monday, January 15, 2001 7:25 AM > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: Re: [PIC]: EE challenge PIC && 12V battery > > GMorbe wrote: > > > > Hello Roman, All > > > > I think i go the discrete approach because of components availability > > reasons. > > The use of a capacitor for the hold time is clever but i dont like it, > > because the PIC would die down slowly by discharge unless you take > special > > action to avoid this. > > Meanwhile i found a solution around the diodes to decouple the button > > information from their switch on function. By connecting the buttons to > > the - potential its possible to decouple them with resistors only. The > > values of them needs to be well defined however. See my picture. > > > > Germain Morbe > > Hi Germain. I'm not sure I like the design. Your 12v > battery voltage is permanently connected to the two > PIC pins, which: > 1. is way out of voltage spec!! > 2. will drain battery into the PIC protection diodes. > > Why not replace the 10M with 1N4148 glass diodes, these > are cheaper and smaller than resistors, and will > solve the two problems... > -Roman > He would also need to provide pullups from the PIC side of the diodes to Vcc, otherwise there would be nothing to pull the PIC pins to a logic one if a button wasn't pressed. Mike -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

you can ditch the left hand transistor and it's associated bits if you turn one of the button reading ports round to be an output once you have read it. Just use the PIC pin to pull the line low... would need to ditch the 10M resistors too though. replacing the 10Ks with say 220k would reduce off current, if your transistor has enough gain. connecting 1n4148s or similar from the button pins (anode) to vcc of the pic (cathode) will ensure the voltage on the pic pins remains within spec, although if you check the datasheet hard enough you might find that the protection diodes are able to perform this function safely (personally i would use external diodes) (the radio is constantly powered at the moment btw, which I assume is just an error in your schematic ?) a handy tip for optimising low power stuff: measure the current being drawn from the battery with a well calibrated meter and hack your code to make the unit operate either constantly on or off (you need to do both) then try disconnecting bits of the circuit you think you can optimise and see if they actually make a significant change to the current draw. if there is no big change then don't waste your time. (useful for instance in verifying if the 'off' current of your circuit is acceptable / improvable) regards, Simon -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Simon, according to Roman ( and he4s right by the way ) the portpins are not real oct because of the protection diodes as you found also. Therefore pulling the base low after a button was pressed would work, but releasing it to high state ( what means 12V in this case ) would probably not. Also changing the 10M resistors to a significant lower value would result in exessive current drain while in off state. Roman, i will decide to use the diodes or not after i finished my messurements. I took the idea for the simplification out of a MCHIP appnote about interfacing a pic to the AC powerline via just one resistor. I found if thatone worked my should also. Germain -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

germain: >but releasing it to high >state ( what means 12V in this case ) would probably not. doh. of course it wont. my apologies. could use could use a series diode to fix it of course, but then the circuit complexity is creeping up again without offering any advantages over what you already had. regards, Simon -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Be carefull with that one resistor to full AC voltage - you'll get away with it on 110V RMS systems, but 230V (peak way over 400V) systems *WILL* destroy the resistor in time. The solution is to use 2 equal value resistors in series so that each experiences less than 300V peak (their design limit). This is a global discussion group so designs and FAQs *SHOULD* always take into account that most of the world now uses the nominal 230V standard. (Are you listening Microchip ?). Bye. > {Original Message removed}

On Tue, 16 Jan 2001 08:36:46 +1100, you wrote: >Be carefull with that one resistor to full AC voltage - you'll get away with >it on 110V RMS systems, but 230V (peak way over 400V) systems *WILL* destroy >the resistor in time. The solution is to use 2 equal value resistors in >series so that each experiences less than 300V peak (their design limit). ..or use metal glaze resistors, which are deigned for high voltage use. >This is a global discussion group so designs and FAQs *SHOULD* always take >into account that most of the world now uses the nominal 230V standard. >(Are you listening Microchip ?). -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu