whats wrong with using a quality DMM for a good, highly isolated measurement?
I could do but I want to be able log the data to sd card/computer, thought about 8 data loggers or 8 meters with usb output but not found any thing to suit really so I think it's better to design your own plus you get the buss of designing it and a good challenge.
Unclebog thank I will have a look into that way.
The idea is I want to measure 8 different voltage's from 8 different units to a main control room to monitor and set of alarms if threshold is reached either way (high/low). rather than having 8 separate units to look at just have one screen later on they might consider Bluetooth modules again having single unit make it easier and cheaper in the long run. Not sure if we will be using PIC24/32 or even the LPC1768 as this would be an on going development and more features could be added.
hope this make it a bit clearer in what I'm trying to do.
The ADuM6401 in my schematic at #3 integrates the whole DC-DC switching regulator so that only smoothing capacitors are required externally. The downside is that the power available on the isolated side is limited to a few hundred mW. Old_but_Alive's ADuM3473 requires more external components but consequently can supply more isolated power. I designed that circuit 4 years ago and I can see that Analog Devices have added more digital isolators to their range, plenty to choose from.
There will be no current required really as I only want to measure voltage up to 35 volts max it would be so easy IF we could join all the grounds together but this would be impossible as they would effect each other (already tried it
) Posted on: January 08, 2014, 09:26:18 21:26 - Automerged
I've had a quick look at your way unclebog and the down fall I can see with that is I want to use 1 micro to measure the 8 channels at the same time not sure if it is possible to use 8 A/D converters with 8 SDA/SCLK to one micro to transfer the data. Let's say the measuring board needs to convert the 0-35V signal to 0-5V one for each unit required and these will have there own 5V supply. then I need to send that 0-5V some how (isolated) to one master unit using the micro ADin inputs. So would the HCNR201 chap be better if it give 12/13bit's as the micro A/D is either 10bit or 12bit. accuracy can be 50-100milli volts either way. I've had a quick look at the digital isolators but my understanding is they only transfer logic signal am I correct ?
This is looking like to be a bigger challenge than I first thought
Thanks to everyone for all the good ideas and they look very interesting and my suit other applications