Propeller Proto USB Problem

Sal Ammoniac

I got my Propeller USB proto board today and it's not working as expected.

I'm using a 9v DC 300 mA wall-wart power supply (2.1 mm coax connector, center positive). The green "power" LED comes on and stays bright for about 10 seconds when I flip the switch, and then gradually fades.

Here's what I see with my DMM: input voltage is 8.97v at first, then drops to 2.8v gradually over a 10-15 second period. The green LED gradually dims, but never goes completely out.

Output of the 5v regulator is 5.02v when the switch is first turned on, then drops to 2.2v after about 10 seconds.

Output of the 3.3v regulator is 3.29 at first, then drops to 1.2v

I have nothing else connected to the board, not even the USB cable to the computer.

Any idea what may be going on here? is a 300mA PS enough for a bare proto board? Could there be a short somewhere? (But if there is, I don't see why it takes 10 seconds for the voltages to sag.) The regulators and the Propeller chip don't even get warm to the touch.

shanghai_fool

Sal,

I think the 300ma power supply isn't quite large enough or isn't really putting out 300ma. @ 9VDC. I use a 7.4V@2A which works quite well.

Don

Sal Ammoniac

Found the problem. The 10uF filter cap near the 5v regulator was either installed backwards, or had excessive leakage. Whatever it was, it was enough to pull down my 300mA power supply.

When I connected a 9v battery to the board, the cap fried itself and left me sitting in a room full of foul smelling smoke. Once I removed the lump of charcoal that used to be a capacitor the board worked just fine. I'll replace the bad cap with a new one in the morning.

BradC

Sal Ammoniac said...
Found the problem. The 10uF filter cap near the 5v regulator was either installed backwards, or had excessive leakage. Whatever it was, it was enough to pull down my 300mA power supply.

Don't forget to let Parallax know they have a problem in their process that let that slip through. If you don't tell them, they'll never know. And to be honest if you contact them directly they'll probably replace the board for you.

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If you always do what you always did, you always get what you always got.

Michael O'Brien

I second that, I have 15 proto boards (non-USB) and 9 USB boards and have no problems with any except one through hole that was blocked and let them know. Remember Parallax sales staff is excellent.
/michael