Trying to use all four channels with an ADC0838 and having issues with software.

Turnbull2112

I have been reading other threads about using the ADC0838 and I am having trouble getting all four differential inputs to work. I would rather use this instead of three or four ADC0831's to conserve I/O and also to keep costs down. Any ideas??

Thanks
-Rob

Mike Green

As with most questions of this sort, we need more information. At the very least, you need to post a schematic or detailed description of how you have your Stamp and ADC0838 connected and a copy of your source code, all provided as attachments to a message. Use the Go Advanced button and you'll see a button for adding attachments to your message. You also need to describe what kind of trouble you're having.

Turnbull2112

Sorry Mike,
Here is my test program so far. What I gather from other threads is that I need to tell the ADC0838 to return information from each differential input (1,2,3,4) with a binary string but I am not getting any results. The datasheet shows instructions to be sent for address, polarity of each input, etc. My experience is limited to the ADC083. What I am trying to do is to read three analog inputs with one ADC0838. I would like to have three subroutines that control this and return the three readings. Is this possible?

Turnbull2112

Ooops, *experience is limited to the ADC0831.

Turnbull2112

Just thinking some more, I would like to see something like this:

DO
GOSUB read_channel1
GOSUB read_channel2
GOSUB read_channel3
LOOP

read_channel1:
read ADC0838 differential input 1,2
RETURN

read_channel2:
read ADC0838 differential input 3,4
RETURN

read_channel3:
read ADC0838 differential input 4,5
RETURN

Does this help?

Mike Green

As you can see from the datasheet, the ADC0838 is very similar to the ADC0831 except that you have to provide the 5 bits of control information as shown on pages 11 and 14 of the datasheet. Your little test program in message #3 should work using inputs CH0/CH1. What's happening? How do you have the ADC0838 connected? What's being returned?

Turnbull2112

I think I had some jumpers in the wrong place. I am getting data back now but it's a little strange. I'm reading differential inputs 1,2-2,3-3,4 to give me three voltages. Right now if I supply 5v to input 1 the debug returns "255,128,128" even though input 2 and 3 + is disconnected. If I connect only input 2 + debug returns "0,255,128". Where is this "128" coming from? Is this a timing issue?? All the negative inputs are common.

Turnbull2112

I'm probably just going to use three ADC0831's. This thing is a pain in the butt.