A digital Multimeter provides a strong basis for the development of a Basic Electronics principles and applications course.

VIDEO: https://we.tl/t-FRPuvyCaMz

This is part of an 8-week course on the basics of electronics for beginners. The final laboratory is soldering and testing multimeter as well as coding and testing it. A basic working microPython program (110 lines of code) has been developed to handle all the basic calculations (ADC values) as well as displaying these values on a quad 7-segment display.

The current version uses THT technology to help students get some experience soldering.

SW1 - Switch1 is used to POWER on/off the multimeter when it is connected to a 9V battery.

SW2 - Switch2 is used to switch between programming the Raspberry Pi from the USB or using BATTERY to power the device.

Warning: set this switch to USB if programming the Raspberry Pi, otherwise set this switch to BAT when connecting your device to a 9V

battery.

SW3: When measuring Volts, set this to Volts, otherwise set this to the milliAMPS current setting

SW4: When measuring Volts you can adjust the range to 1000mV (max) or 10V (max) measurements.

SW5: To let the Raspberry Pi know you are measuring Volts or Current (Amps). The default setting is Volts due to an internal pull-up resistor.

Safety:

There is a replaceable 1000mA fuse is things get out of control.

A 3.0V zener diode (D4) is used as a reference voltage on the ADC-ref input (after measuring it once installed it measured 2.74V)

A shottky diode (D3) is used to prevent current returning to the Battery. This reduces the 5.5V supply down to 5.25V to the Pico

A Diode (D1) is used for over current protection, buu was not used in this design.

VIDEO:

hopefully this works....but I have a video of this multimeter: https://we.tl/t-FRPuvyCaMz

I uploaded it to WeTransfer. It is about 170MB !! (note:Anson help upload the video in youtube)

microPython code

You will need to rename the file to Main.py before the pico will run it upon boot-up.

You can make minor changes to the conversion factor based on the accuracy of your components.

The current Raspberry can work with or without the 3V zener diode as a reference for the ADC. The current partnumber provides a 2.74 reference for some reason. So you will need to adjust the conversion factor from 3.3V to 2.74V.

Suggestions for improvement:

Find a better 1 Ohm sense resistor then the current version. The current version uses 2 parallel 2-Ohm resistors to allow for more current, but compromises on accuracy. The probes are currently used for both VOLT and Current measurement which allows for an efficient design but has some drawbacks. Some of the current probes and connectors could be improved. the 9V battery connector to the board needs a better interface - and can come lose with heavy use. The probe cables currently use alligator clips but may be nice to have interchangeable probes.There is no auto-detect or dynamic scaling capability for better display ranges. This can be improved with some minor hardware and software changes. The next iteration will be with 1206 SMD components