Use PIC16f877A to turn on relay and magnetic valve.Why MCu hot?

[Mikebits]

See why it helps to draw schematics. Can't see how you could heat up a 16F877 with a 10K on VDD though. Do you have decoupling caps? Both VDD & VSS connected? Stable regulated 5V?

Maybe it is current starved and oscillating? Who knows ???

Never used a PIC, do they go into wierd conditions with funky power?

Last CPU I designed with was the mobile pentium. Damn pain in the arse part.

 

[arunb]

You have not shown how the PIC is connected to the supply, an EXACT schematic is essential if you want to solve the problem.

thanks
a

 

[babboy12345]

why must put a decoupling caps at both VDD & VSS

 

[Mikebits]

You did not answer my previous question about the 10k resistor. You do not need decouple caps on your ground pins, You only need decouple caps on your power pins ie. +5v
I think Blu meant caps connected from power to ground.

 

[babboy12345]

now i remove the 10k resistor at the Vin place.Initially i do this is to protect my MCU burned.

 

[Mikebits]

now i remove the 10k resistor at the Vin place.Initially i do this is to protect my MCU burned.

So have you tested it yet? What happens now?

 

[blueroomelectronics]

You need decoupling caps with any digital logic IC. 0.1uF is common. We can't help you until you provide a complete schematic of your design. Photos may help.

 

[babboy12345]

i try it whole day,i figure out somethings.That is,my MCU circuit and relay all no probelm,works well.Even i use relay to turn on 240V without load(mean valve),its still work.But if i connrct the 240 to my valve,problems happen.MCU hot and MCU stop function.i am using 220v ac 50hz solenoid valve.is than my valve problems???

 

[blueroomelectronics]

I'll type slowly.

You need to draw a COMPLETE schematic of your project. Our crystal balls are on the fritz.
**broken link removed**

 

[babboy12345]

but i dono how to draw it........

 

[blueroomelectronics]

I would say it's a good time to learn. Eagle CAD is a good drawing program.

 

[Sceadwian]

Better learn babboy =) Text description are almost completely useless for anything more than a couple of connections. Try just jotting down all the electrical connections as you have them hooked up using standard symbols. Do it on paper and scan or photograph the paper if you can't do it on a computer.

Electronic symbol - Wikipedia, the free encyclopedia
There's a good starting point.