Problem with PIC16F87

[dhouston]

I'm afraid I don't grasp what the 555 is doing. Do you have a link to the website where you found the 555 circuit?

[The Master]

Sorry, I just realised that schematic is slightly wrong. The POT should connect to pin 7. Its connected right on the PCB though.

Ive uploaded the corrected schematic. I found the website i thought i got it from but it seems i didnt use that one (i dont think i got it to work). The circuit i used is one of the example circuits in PCB Wizard. Ive uploaded a screenshot of that too.

In my circuit ive used a 15K resistor and a 5K POT in series instead of the 100K VR in the example and ive used a 1nF cap instead of 100uF

[Melanie]

No Resistor from the 555 to the Base of the Transistor? How hard do you want to turn that poor Transistor on? If you disconnect pin 3 on the 555 and still have your 7805 (they DO need a heatsink) overheating, then you've damaged your 555.

[The Master]

Thats another mistake, sorry. There is a 10K resistor between pin 3 on the 555 and the base of the transistor.

I use 7805s in every circuit i make that needs 5V and they never need a heatsink. Sometimes they do get slightly warm if a lot of things are running from them but still not enough to need a heatsink.

For testing i moved the 555 to a breadboard with a seprerate regulator and that regulator stayed cold. The one on the main board still got hot though which means its the IR emitters that are causing it to overheat. According to the datasheet they should be drawing 100mA each. Theres 2 of them but its about a 50% duty cycle so i would expect the average to be around 100mA. Lastnight my multimeter showed 102mA for the emitters and the 555 so i guess thats about right then as long as i put a heatsink on this regulator.

[dhouston]

I see Data A & Data B but no GND for the RS485 network.

[The Master]

The RS485 ground is the same as the ground for the rest of the circuit (0V)

[dhouston]

Try it with the RS485 network disconnected. If the current drops, then use a 100 ohm, 1/4W resistor between the RS485 GND and this circuit's GND.