Need for 8 -channel current measurements (AIN0-AIN7, 4..20mA)


I have a Rabbit SBC BL4S100 hardware. I have read from the user manual how to set up the A/D converter inputs AIN0-AIN3 for current measurements (4…20mA), by setting the jumpers on header J10 and J11.

So, my question is that is it also possible to use the AIN4-AIN7 for current measurements, because my application needs to use all these A/D inputs?

In channels AIN0-AIN3 there is the parallel 100ohm resistor, so perhaps I just need to add external resistors also for AIN4-AIN7?

br. Kari Lindgren

I reply to this thread myself, because no one has done it yet :wink:

I was testing with the BL4S1xx.lib functions and found that they do not support other channels than 0…3. If I try to config e.g. channel 4 for current measurement, the function will generate a runtime error.

anaInConfig(channel, mAMP_MODE);

I have to dig in more with the library function source codes.

br. Kari L

The BL4S100 ADC only measures voltage. Those inputs which are configured to measure current simply insert a resistor from the voltage input to ground. You can do the same thing on the other channels. If you insert a 100 ohm resistor, you can still configure the A/D to measure voltage. In this case 20ma will yield 2V.