Board works only when connected to serial

[jsimpson001]

I have created my own PCB which works fine when connected to the computer's serial port, but functions oddly when it is disconnected.

Any ideas as to why this might be?


Thanks a lot

 

[Mycroft2152]

Time to bring out the crystal ball, folks.

J,

How about givng us a little hint like a cricuit diagram or a picture of the pcb? Perhaps the moon was in Aquarius.

All kidding aside, you haven't given us anything to on.

Myc

 

[premelec]

I'll second the above - also do you have the 10K/22K resistors on the PCB so that the serial input is not left hanging open when you disconnect serial? ALL inputs not used must be tied to a power rail to prevent elec noise pickup -what's happening?

 

[jsimpson001]

Pictures

Here are some pictures.

 

[Mycroft2152]

The pictures are helpful.

I would forst look for any cold solder joints. There are a few that look questionable.

Also, what does "functions oddly" mean.

Myc

 

[testerrrs]

Floating serin pin?

 

[jsimpson001]

Floating serin pin?

The serin pin is at 3.5v when connected to pc, 2.5 when not connected.

Do i add a pull-up resistor?

 

[Mycroft2152]

Did this work correctly when you breadboarded it?

 

[jsimpson001]

yes it did.

 

[testerrrs]

The serin pin is at 3.5v when connected to pc, 2.5 when not connected.

Do i add a pull-up resistor?

The serin pin should be pulled low when the download network is not attached, a 4k7 will do the trick.

Jon

 

[jsimpson001]

It now works, it was a floating voltage on one of the input pins.


Thanks a lot for your help

 

[hippy]

Some indication of what we're looking at would help. As best I can see it's two PICAXE's with two programming sockets. It looks like at least one of the programming sockets is wired wrong.

Sorry for the poor quality image but the forum file attacher rejected it otherwise and I wasn't going to spend any more time on it.