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DIY Modular Test Equipment Project
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Kleinstein:
One can also do classical counting with an µC. AFAIK the PICs are quite good at this. Other µs might need a little extra HW to get to higher frequencies. AFAIK some of the PIC18 include hardware that is supposed to be useful for analog time interpolation with relatively little additions This would give a rather high resolution reciprocal counter (e.g. sub ns resolution) with moderate effort.

Usually reciprocal perform better than simple classical counters, as the resolution is no longer limited to fixed increments of 1 over gate time. Its only at the upper limit that both ways have about similar performance.

Many other function would need an µC anyway - so I see no big advantage in avoiding an µC for a counter, if this is something the µC can do very well.
void_error:

--- Quote from: Kleinstein on December 31, 2017, 05:31:01 pm ---One can also do classical counting with an µC. AFAIK the PICs are quite good at this. Other µs might need a little extra HW to get to higher frequencies. AFAIK some of the PIC18 include hardware that is supposed to be useful for analog time interpolation with relatively little additions This would give a rather high resolution reciprocal counter (e.g. sub ns resolution) with moderate effort.

Usually reciprocal perform better than simple classical counters, as the resolution is no longer limited to fixed increments of 1 over gate time. Its only at the upper limit that both ways have about similar performance.

Many other function would need an µC anyway - so I see no big advantage in avoiding an µC for a counter, if this is something the µC can do very well.

--- End quote ---

It seems that I have implemented a reciprocal counter. Didn't know it was called that.

I guess I'll be sticking with a MCU in the end. Found this neat little document.

For anyone not wanting to use a PIC there will be the possibility to put their own MCU on a daughter board.
void_error:
I've almost finished everything needed for the waveform generator / frequency counter as far as schematics go, with the electronic load and lab power supply not far behind. Depending on how things progress I might have stuff on GitHub this weekend.

One thing I've settled for is using 3.3V for the logic and +/-3.3V for the analog stuff where digital isolators aren't used, the only exception being the AD603 used to adjust the output amplitude of the waveform generator's output for sine/triangle which requires +/-5V, delivered via a pair of LM317L/LM337L off the +/-15V supply of the output stage.

As far as the electronic load and lab power supply are concerned, they're 80% done unless I find easy ways to add more features which I've been doing a lot lately at the expense of them not being finished yet (like another multiplexer for the option to measure all the internal supply rails). :scared: Oh, and it's 80% of the schematics, PCBs not included.

Speaking of PCBs, that's another can of worms since it's about a dozen of them... almost:

* UI board
* Waveform Generator & Frequency Counter
* Lab Power Supply
* Electronic Load
* Front Panel & Aux Digital Channel
* USB Charging Module
* USB - UART interface
* Aux Analog Supply (linear regulators - easy)
* Aux Digital SupplyOk, it's only 9 of them.

Another thing I have planned for sometime in the future is an ethernet module based on some PIC18 and Microchip's TCP/IP libraries but I'm not going too far with it from the start and I'll probably base it on an existing example.

One thing I still have to look into is whether I can reuse the Front Panel module designed to be used with the lab power supply for the electronic load as well, without the relays used to switch the two channels between independent/series/parallel and for that I have to decide what the high current range will be and what connectors I'll use and whether they'll be PCB mounted or panel mounted. Looking for parts is very time-consuming, especially when I'm trying to stick with only 2 distributors - TME & Farnell. Digikey and/or Mouser will have everything anyway but shipping cost will be higher for me at least.

If anyone has any comments or questions or pretty much anything related you can leave them below. Blame the way the forum works if they end up on the next page (joking). :blah:
bg9gas:
 :-+ :-+ :-+ :-+
xani:
For ethernet side honestly you're probably better off just sticking raspberry pi there, it has serial, SPI and I2C on it, it's cheap, and you can then run any data acquisition directly in the system instead of pushing data to dedicated PC. Or even run a web UI with modules state/controls

For IDing modules daisy chaining is probably easiest option, but you should also probably have modules send their name and some unique ID if a micro has it) with it. That makes it possible for code to work regardless of which order modules are put in or even (if unique IDs are used) if you reorder stuff for whatever reason. Of course, that requires a micro per board

If you go with micro per board it would also be worth to add a single LED dedicated to identify function, that allows for making queries like "which board is ADC number 4" or "which board is one with ID 413e6f"

Or go even fancier and put RGB led on, then you can do "connect left channel to green input, and right channel to purple one"

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