Post by thread:[PICLIST] transistor on input

I am trying to get a continuity check from a 9v battery so I am using a 2n3904 transistor. The PIC is connected to the collector (as it is in the PIC'n example). I am getting the old floating pin deal that I am so used to, so I tried a pull-up, but that just pulls the input pin up to 5v all the time, I can't get a 0. Also I can't figure out why I should use the collector for the input pin instead of the emitter. And last but not least, a few months ago Alice Campbell made reference to an IR to rs-232 dongle, but she has disappeared. Anybody know how to get ahold of her or the details on this dongle?

Alice is having trouble sending to list but is still receiving it OK. She may be contactable at spam_OUT1502amcTakeThisOuTlo.scseng.com She will have received this message from the list but may not have read it. > I am trying to get a continuity check from a 9v battery so I am using >a 2n3904 transistor. The PIC is connected to the collector (as it is in >the PIC'n example). I am getting the old floating pin deal that I am so >used to, so I tried a pull-up, but that just pulls the input pin up to >5v all the time, I can't get a 0. Not sure of your circuit but this will/should work. NPN transistor. Two input probes A and B Input A via 100K resistor to transistor base Input B to PIC Vcc (perhaps via eg 10K resistor for safety) Transistor emitter to ground 100K resistor from transistor base to ground. 10k resistor (or 100k) from transistor collector to Vcc (+5v) Transistor collector to PIC pin configured as input PIC pin will go low when there is continuity between leads A & B. This will work up to "continuity" resistances of about 500K To reduce sensistivity reduce the base to ground resistor. Roughly: If continuity resistance is X and base to ground resistor is R then with values above and 5v supply R = 0.14X + 14 or X = 7R - 100 All resistor values in Kohm For a device sensitive to only small continuity resistances make the 2 base side resistors about 1K ohm. Reducing base to ground resistor will require a smaller unknown resistor to operate. I can comment firther if this isn't clear enough. > Also I can't figure out why I should use the collector for the input >pin instead of the emitter. > And last but not least, a few months ago Alice Campbell made >reference to an IR to rs-232 dongle, but she has disappeared. Anybody >know how to get ahold of her or the details on this dongle? > regards Russell McMahon _____________________________ What can one man* do? Help the hungry at no cost to yourself! at http://www.thehungersite.com/ (* - or woman, child or internet enabled intelligent entity :-)) From other worlds: http://www.changingourworld.com http://www.easttimor.com http://www.sudan.com

> >Not sure of your circuit but this will/should work. >NPN transistor. >Two input probes A and B >Input A via 100K resistor to transistor base Try 1k here, not much base current happening! >Input B to PIC Vcc (perhaps via eg 10K resistor for safety) Try 1k here as well, same as above >Transistor emitter to ground >100K resistor from transistor base to ground. >10k resistor (or 100k) from transistor collector to Vcc (+5v) 10k, or even 4.7k -- http://www.SpamWhack.com A pre-emptive strike against spam A tornado is a lady whose skirts you do NOT want to look up! Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9

{Quote hidden}>>Not sure of your circuit but this will/should work. >>NPN transistor. >>Two input probes A and B >>Input A via 100K resistor to transistor base > >Try 1k here, not much base current happening! > > >>Input B to PIC Vcc (perhaps via eg 10K resistor for safety) > > >Try 1k here as well, same as above > > >>Transistor emitter to ground >>100K resistor from transistor base to ground. >>10k resistor (or 100k) from transistor collector to Vcc (+5v) > >10k, or even 4.7k Yes, could use all sorts of different values of course, but the usefulness of all the above depends on the highest resistance that wants to be considered to be a continuous circuit. High values above work OK with typical beta transistors (150+), will work with values up to ?100's of K (number was discussed in original post). I gave suggested lower values IF a low value was wanted for continuity. The high values have the great bonus in general use of providing a degree of protection for the circuit . 100K will (well, MAY) survive briefly testing the continuity of the AC mains :-) (voltage rating of the resistor becomes important as well as wattage) whereas 1K definitely won't. The 10k (or more) collector resistor is to ensure that the transistor need not have too high a beta. RM

********************************************************************** * This is an automated message. * * This email message has been delayed due to a major system failure. * * We apologise for any inconvenience caused. * * Please ignore any duplicate messages. * ********************************************************************** Alice is having trouble sending to list but is still receiving it OK. She may be contactable at .....1502amcKILLspam@spam@lo.scseng.com She will have received this message from the list but may not have read it. > I am trying to get a continuity check from a 9v battery so I am using >a 2n3904 transistor. The PIC is connected to the collector (as it is in >the PIC'n example). I am getting the old floating pin deal that I am so >used to, so I tried a pull-up, but that just pulls the input pin up to >5v all the time, I can't get a 0. Not sure of your circuit but this will/should work. NPN transistor. Two input probes A and B Input A via 100K resistor to transistor base Input B to PIC Vcc (perhaps via eg 10K resistor for safety) Transistor emitter to ground 100K resistor from transistor base to ground. 10k resistor (or 100k) from transistor collector to Vcc (+5v) Transistor collector to PIC pin configured as input PIC pin will go low when there is continuity between leads A & B. This will work up to "continuity" resistances of about 500K To reduce sensistivity reduce the base to ground resistor. Roughly: If continuity resistance is X and base to ground resistor is R then with values above and 5v supply R = 0.14X + 14 or X = 7R - 100 All resistor values in Kohm For a device sensitive to only small continuity resistances make the 2 base side resistors about 1K ohm. Reducing base to ground resistor will require a smaller unknown resistor to operate. I can comment firther if this isn't clear enough. > Also I can't figure out why I should use the collector for the input >pin instead of the emitter. > And last but not least, a few months ago Alice Campbell made >reference to an IR to rs-232 dongle, but she has disappeared. Anybody >know how to get ahold of her or the details on this dongle? > regards Russell McMahon _____________________________ What can one man* do? Help the hungry at no cost to yourself! at http://www.thehungersite.com/ (* - or woman, child or internet enabled intelligent entity :-)) >From other worlds: http://www.changingourworld.com http://www.easttimor.com http://www.sudan.com