Would anyone like to review for me? I’m working on a 16 bit analog input, 4 channel, SPI or I2C.
Right now I have a rough draft of it set up for 4-20mA readings. This is very useful for using cheap industrial transmitters as sensing elements for inputs to arduino or beaglebone.
Do you have any requests? I could make the board split…2x voltage, 2x 4-20mA input.
I haven’t ever done PCB manufacturing before, but I think a lot of people have this problem. Actually, I’m trying to control some chocolate making equipment, and needed to come up with something. The solution I want should be easy to use.
This is my first whack at this. I’m using 2x LM358N’s ($0.55), a 2N3906 ($0.20) and a 4N35 ($3.08) high linearity opto coupler. It is also very linear. Opto makes the circuit safe for the microprocessor input… I haven’t placed the ADC on the board yet. I’m working in ExpressPCB. As an alternative, I think it would be interesting to make half the board 4-20mA inputs, and leave the other half open to experimentation. It looks easy to get the cost per channel down to about… $10 built. Also would be easy to do a single channel board with AD7988 and some modest changes.
This is my first board so if it sucks, shout it out! I don’t understand why 10bit is the defacto analog input in the makerspace!
Alternatively, if you would like to help me actually produce the first few, then we could do a kickstarter and make some more. If you are a software guy, I’d love to provide this with example code.
I guess I want a 4-ch optically isolated 4-20ma input to reach the uC with good resolution, reliably. I attached a schematic in png format.
My application is reading the temperature of some chocolate coating equipment in my family’s candy shop. I already have 4-20ma transmitters for temp, so it is very easy for me to use and calibrate them. I need to know the temperature of a heated water bath and a mixed chocolate reservoir.
The reason that I need the resolution is because to get good control of the shine on chocolate, it needs to be ‘tempered’ and using a little control script I am trying to have it ready for us when my dad heads in to work in the AM.
If the program you are using is not directly affecting the PCB, then you are not doing it right. You need to make the schematic in the program and the program will transfer that to the PCB with “air wires.” If you are trying to make a PCB while reading a schematic, you are going to get into trouble.
In my personal opinion, if I seen a board designed that way, I would run away from it. Have you ever looked closely at a professional board? Even seen a design for one?
Look at the attached image. Notice the routing of the traces…
Ok, I think I understand what you want to do which is opto-isolator the 4-20mA signal and then convert to digital with an ADC. Unsure of the circuit you posted but codlink is correct, you need to draw the schematic in ExpressSCH and then do the layout with ExpressPCB. Do read the getting started tutorial for these programs. The ExpressPCB can be linked to the ExpressSCH files. There is also a PCB layout guide you need to study and then practice doing the schematic and pcb.
Thanks for the excellent feedback waltr & codlink!
Because eagle lite seems to have a better selection on components to start from, ergo the SCH is in eagle lite. I have a schematic, which is attached. I’ve yet to read the layout guidelines, but I will in the next couple of days. Some of the wires don’t seem to connect right in eagle when I move to layout components, but this is clearly a problem of me needing to read the manual.
Here are the links to the manuals for a few components of the board, as much for my reference as anyone reading this later.
