PICs and harsh environments

[Ioannis]

Yeah, GND must be Vdd...

Ioannis

[erice1984]

yea, no idea what i was thinking when i threw those together, I had it differently just read my notes wrong, really wrong... anyhow, look at this one

[erice1984]

lol, forgot to hook up Q4.... anyways it should be connected to an LED.

[erice1984]

really not liking the CAD software I am using, its tough to read.

[mister_e]

Definitely better, but... Q1 and Q2 are not connected the proper way, the emitter should go to GND, I'll assume a lack of sleeping for this one

I would suggest few things

1. add a 0.1uF capacitor at the regulator input
2. assuming Q3 drive a relay (because i'm not sure of the symbol you're using), I would suggest, if at all possible to use a 12V relay, this will keep spikes far of the logic Vdd. OR, depending how much current your relay coil need, and if have tons of those, add a resistor in serie with the 12v line...
3. D1 is a good idea as long as your load on J4 don't overload the maximum forward current, which is ~1A.
4. Depending how much current and where your LED take it's voltage, you may don't even need Q4

[erice1984]

You are right about Q1 & Q2 they are supposed to be connected to 5v not gnd.

Q3 is driving a relay, that is National Instruments idea of a relay symbol and it pulls about 40mA

J4 will have about 140mA

The LED is actually an incandescent bulb needing ~12v 80mA

[Dave]

erice1984, The way the schematic is drawn the emitter and collector of Q1 and Q2 need to be reversed...

Dave Purola,
N8NTA

[mister_e]

For 140mA drive, could the relay be replaced by a Mosfet or transistor instead?

[erice1984]

erice1984, The way the schematic is drawn the emitter and collector of Q1 and Q2 need to be reversed...

Dave Purola,
N8NTA

Aye, Thanks for pointing that out, Q1 and Q2 are correct, I have the resistors connected incorrectly, they should be hooked to ground instead of the 5v that the diagram is showing..