Multimeter
Making my own multimeter since I don't have one
Created by
Shaan
Tier 5
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Shaan
added to the journal ago
Created schematic
After doing some research I decided to go with a STM32 chip to power my multimeter, more specifically, the STM32G431CBT6. It has a fast ADC, supports many peripherals, and is reasonably priced compared to other options
For my power I'm gonna use two AA batteries to power it. But because batteries slowly lose their voltage while being used, I need a boost converter to keep the output stable. I placed my multimeter's on/off switch (S1) right before it gets used by the circuit.
My USB-C receptacle will be only used for programming, as I don't really see the point of having a multimeter powered with usb-c only and it'll add unnecessary cost for switching power inputs.
For my voltage sensing, I'm going to use a resistor divider to scale down the higher input voltages into a safe range for the STM32. For resistance and continuity testing im using a mofset controlled path, I can have them as the same since to measure continuity all the code needs to do is check if the resistance is below a small threshold
The 5amp input uses a shunt resistor so that the STM32 can measure the voltage drop and calculate the current
I forgot to add an actual rotary function selector switch until now, so I'm just gonna add the symbol and hook it up to my STM32. The 4 functions you can select are Voltage, Ohms, Amperage, and Continuity. I also then realized that I didn't have a buzzer yet, so I quickly added that too.
Unfortunately since I couldn't find any cheap rotary switches that fit my needs online with a good datasheet or with available footprints/symbols, I decided to just scrap the rotary switch alltogether and I'm gonna use four buttons instead (Continuity, Voltage, Amperage, Resistance).
Assigning footprints was quick and simple, I used slightly larger components like resistors and capacitors to make it easier for me to hand solder them. I will get PCBA to solder my STM32 and other complex components as I don't have the soldering equipment or expertise to solder those things reliably.
Shaan
added to the journal ago
Created base model
I want to base this multimeter off of a Fluke 117 since I like how they look, so I got similar dimensions to one, and created the knob so far. I still need to find a display thatll fit my project, the only thing I could get so far is two mini LCDs pushed together, which doesnt look great
Shaan
started Multimeter ago
12/7/2025 - Created base model
I want to base this multimeter off of a Fluke 117 since I like how they look, so I got similar dimensions to one, and created the knob so far. I still need to find a display thatll fit my project, the only thing I could get so far is two mini LCDs pushed together, which doesnt look great
1/31/2026 - Created schematic
After doing some research I decided to go with a STM32 chip to power my multimeter, more specifically, the STM32G431CBT6. It has a fast ADC, supports many peripherals, and is reasonably priced compared to other options
For my power I'm gonna use two AA batteries to power it. But because batteries slowly lose their voltage while being used, I need a boost converter to keep the output stable. I placed my multimeter's on/off switch (S1) right before it gets used by the circuit.
My USB-C receptacle will be only used for programming, as I don't really see the point of having a multimeter powered with usb-c only and it'll add unnecessary cost for switching power inputs.
For my voltage sensing, I'm going to use a resistor divider to scale down the higher input voltages into a safe range for the STM32. For resistance and continuity testing im using a mofset controlled path, I can have them as the same since to measure continuity all the code needs to do is check if the resistance is below a small threshold
The 5amp input uses a shunt resistor so that the STM32 can measure the voltage drop and calculate the current
I forgot to add an actual rotary function selector switch until now, so I'm just gonna add the symbol and hook it up to my STM32. The 4 functions you can select are Voltage, Ohms, Amperage, and Continuity. I also then realized that I didn't have a buzzer yet, so I quickly added that too.
Unfortunately since I couldn't find any cheap rotary switches that fit my needs online with a good datasheet or with available footprints/symbols, I decided to just scrap the rotary switch alltogether and I'm gonna use four buttons instead (Continuity, Voltage, Amperage, Resistance).
Assigning footprints was quick and simple, I used slightly larger components like resistors and capacitors to make it easier for me to hand solder them. I will get PCBA to solder my STM32 and other complex components as I don't have the soldering equipment or expertise to solder those things reliably.