This thing right here, is awesome, and I bet that you want one as well.
This is yet the best multimeter I’ve made so far and let me tell you why. Well, first of all, is
homemade, and that’s awesome, especially knowing that I’ve designed it myself. But second of all,
it is very small but it has a lot of modes. It can measure voltage very precisely. The same for
resistance and also capacitance. And if that is not enough, it can also measure inductance which
usually is a bit more complicated, but this one does it very well. And on top of that we also have
other modes for current measurement, frequency, continuity, pulse generator, diodes and who
knows what other modes I could program for future firmware updates. And on top of that, it also has
a space for a Bluetooth module so we could connect it to our smart glasses project and see the
measurement in front of our eyes, that’s pretty cool, right? Is very easy to use with both hands
and you don't have to place it over a table as you do with common multimeters, that’s very practical.
Is rechargeable with a USB connector and it has battery protection and much more.
I’m sharing all my files with you and also the code as open source in case that you want to
make the same project. So let me show you all the details about this PCB, the code, how it works and
make the entire multimeter. This was more than 1 year of work. So guys, let’s get started.
What’s up my friends, welcome back. Ok guys so remember that I have multiple videos about
such multimeters based on Arduino so make sure you check the other videos because there will
be some parts that I won’t explain because I’ve already done it. Last version of the multimeter
worked pretty well with high precision. But it was a bit ugly, too big and you had to place it
over the table and that’s not too handy. I want to have full use of both hands and be able to
see the measurement all the time so that’s why I’ve made this new version that is very, very,
small and you can use it with both hands while still seeing the measurement in front of you.
Before we go over the code and all the modes, let’s assemble it. With help from PCBWAY
I was able to improve my prototype getting better and better and this is the final PCB.
As you can see, it is very, very small for a multimeter, measuring only 1 and a half cm wide.
So guys, get the GERBER files for the PCB from my website
and then we go to our dear PCBWAY. We click the quote now button and insert the size of the PCB.
I also select the amount of the PCBs and the color of the solder mask, red in my case. Save to
cart and on the next page upload the GERBER files you’ve downloaded from my website in a zip format.
make the payment and in under 5 minutes, the order process is done. The PCBs arrive to Spain
in around 10 days and they look awesome, just as I wanted them to be. PCBWAY always does a pretty
neat job and I sometimes still can’t believe that nowadays you can have prototyping PCBs for only 5
dollars, that helps us creators to develop a product a lot. Ok, now we have the PCB and is
time to assemble all the components. I’ve used a lot of 0402 components which are quite small
and might be a bit difficult to solder, but with patience, everything can be done. You have the
full part list and the values below the video so check it out and buy each separate component.
The most crucial part is the microcontroller, once it works, we can solder the rest.
To make this faster, I’ve took mine out from an Arduino NANO clone, together with the 16MHz
resonator. That speeds up the process and also assures you that the chip has a bootloader.
When you buy a new chip like these ones, they sometimes come brand new, without a bootloader.
Use the hot air gun and take out the chip and the resonator. Take the PCB and we must solder the
ATMEGA328 microcontroller, the resonator, the R30 resistor, the R31 resistor and the C17 capacitor.
We must have these components in order to test the microcontroller.
So place some solder paste and solder the IC. You might need to retouch some of the small pins.
Then add the resistors and capacitors. Then, on the back, solder wires to the UART pins for DTR,
RX and TX together with GND and VCC. Connect an external FTDI module like this one.
To test the microcontroller I always upload a code like this one. In this way,
we make communication with the monitor and print a counter. Upload it and open the monitor.
If you get the counter from the board, that means that the microcontroller works ok.
We can now solder the rest. Let’s solder the battery charging and protection components
which are all these ones here. Also solder the USB connector.
Now get a 3.7V battery and connect it to the battery pads plus and minus.
Check the voltage with the multimeter and make sure everything is ok.
Then connect the USB connector and check if the charging process works.
If yes, we can continue. On the front part of the PCB, solder all the small resistors,
the capacitors, the on and off switch, the ADC chip of 16 bits and the OPAMP.
We also have some small LEDs.
Soldering 0402 components is not that difficult. Carefully solder all the small components.
Then I also add a small push button. Finally we have to add two slide switches.
I’ve ordered this type of slide switch but it arrived at my old place so I had to order it again
and I don’t have it right now. So for this test, I will use these ones but I have to adapt them.
They still have 3 positions and 2 outputs. I’ve took them out from the metal case and shortened
the pins. I will solder them like this so we can slide them at the same time. The reason I’ve used
two switches, is because I wasn't able to find a sliding switch with 3 outputs and 3 lines.
We must have that in order to separate the current mode from voltage mode.
In the previous version I was using a rotary switch to do that.
But that component is very very big for such a small multimeter, so I had to make this approach.
Later, together with a suposables 3D printed case, we will merge these sliding switches
together and they will move at the same time. Ok, solder the rest of the components on the back.
And finally, we can also solder the Bluetooth module.
make sure that you solder a 3.3V regulator for the module, because more than that might burn it.
Check this schematic for all the values and components. You can download it from below.
So, the PCB is ready, all that is left is to add the OLED display.
For that, you can get this kind of screen and just desolder the display from the small PCB.
Then solder that display on our PCB and is ready to go because it already
has the needed components on the PCB. At this point you need to test each part separately.
You have a different code for that on electronoobs.com.
So download them 1 by 1 and upload them to the PCB using the external FTDI module.
For example, download the OLED screen test code, upload it to the PCB
and see if the screen works. If not, maybe change the i2c address in the code
and if that still doesn't solve the problem, well you might need to check the solder connections.
For the probes you will need a cable and two metal pins. I’ll get mine from a cheap
multimeter that cost me only 2 dollars. I solder the metal pin on the tip of the multimeter.
Then I solder the red wire with the probe on the probe pin on the other side of the PCB.
Now we can measure with it, so download from below the final code. ( )
The 3D case is still in progress and since I still have to correct some errors,
I will make the final design in the next part of this project.
Now remove the UART wires. Then we can solder the battery to the battery pads on the back.
Slide the on off switch and turn it on. Slide the switch to the right and we are into voltage mode.
I measure this battery using a commercial multimeter first.
Then I measure it with my multimeter and we get pretty much the same value. Since the input for
voltage has a voltage divider with a value of 11, this multimeter can measure up to 55V DC.
The AC voltage measurement is not ready yet,
since the rectifier I’ve used has a voltage drop that is too big and is not even linear.
Slide the switch to the middle position and we can measure resistance.
I measure a few resistors to check the values. This part has a small error that I must fix.
As you can see, the resistance part in the schematic is connected to some pins used
for the other parts since the RLC negative connection is shared with multiple parts.
During each mode, in the code, I put these pins as input so they won’t interfere. But
for some reason, the OPAMP used for inductance measurement affects the resistance reading.
Ok, press the button once and we enter capacitance mode.
It can measure pretty precise capacitance from 1uF up to thousands of Farads.
The problem once again is for small values. Again, these two capacitors are always connected at the
probes input and we can't measure lower values as we did with my previous multimeter, values
down to 33pF for example. So my bad, I’ve made a mistake of using shared pins. The solution will
be to just use two external ADC instead of just 1, and that’s what I will do for the next part.
Push again and we can measure inductance. I measure a few values.
Push again and we can also measure frequency which is very easy
using the pulse in function in the code and calculate the frequency.
Slide the switch to the left and we enter current mode. I’ve used the ACS712 IC of maximum 5 amps.
I connect a battery in series with a load and measure the current value.
I get pretty decent values. Basically, this multimeter could measure voltage,
resistance, capacitance, inductance, current, continuity, diodes, frequency and also create
square pulses or PWM signals. I’m working on other modes such as transistor measurements.
So, I think that's quite awesome, right? What do you think? The 3D case is not yet ready,
but I will have it soon and I will also fix the rest of the problems, but I think this could be
a very useful product, right? Is small, decent precision for homemade projects, is portable and
rechargeable, it has multiple modes and could still have improvements. I think that the size
is the best improvement from my previous PCB, right? I hope that you like this video and if so,
consider giving me a like or comment below. Thanks again and see you later guys.