This is a sub-project of #Grimoire
I need your help to develop the smallest and cheapest (yet useful) breadboard sniffing tool!
The LED bubble display is cute but quite expensive. With a small LCD as intended, this should be easy to solve.
Now the interesting part is the sigma-delta ADC : the MCP3421 is small and cheap enough, it works as a voltmeter but could also be reused for current and resistance measurements with a bit more electronics (maybe with a MCP3422 that has 2 inputs ?).
The display and CPU aspects should be easy to merge with the rest of the project. An I2C interface is required but if we have a programmable MCU, it's possible to bitbang it.
Shots have been fired...
20$ on sale, in kit version. We're halfway there...
This project is made possible by the very low cost, high volume parts that exist today.
The BOM is < $7 now, about $3 remain for some other special functions.
One microcontroller is required to expand the pin count, provide more flexibility (like selection of the function and upload of the firmware to FPGA) and more interestingly provide some ADC capability. However the MCU's ADCs are not the most appropriate because we need 2 kinds of measurements :
The slow ADC can be created with an ramp generator and an analog comparator, the FPGA or MCU can implement a counter that is compared to a 4.096V voltage reference (or something like that). A NE555 in VFO mode could work.
However the oscilloscope mode requires a fast ADC and a frequency-dependent filter is necessary to avoid aliasing (switched capacitors filter ?). This part and the other analog parts for the Ohm meter can quickly eat up all the BOM margin...
The choice of MCU is not highly critical. Some will want a PIC, others an AVR, others will want something else... It could even be emulated with your own Arduino or Raspberry Pi during development. It could even be a soft-CPU inside the FPGA (but the pin count increases and pushes the price higher). All it has to do is :
Anyway the heart of the system is looking cheap and I can see how to do several desired functions. But I don't think I can do it alone. I bet some people will come up with cost optimisation tricks later, I have to start somewhere...