Multimeter is one of the first items you should have when getting into FPV. In this tutorial I will go through the basic functions of a multimeter, and how to “test your drone” with a multimeter. A multimeter is also sometimes called a DMM (Digital Multi-Meter)
Using a multimeter and smoke stopper to perform electrical checks is an excellent way to prevent electrical damage and magic smoke when powering up FPV drone for the first time.
Table of Content
- Buying a Multimeter
- Multimeter Explained
- Continuity Mode
- Measuring DC Voltage
- Measuring Resistance
- Measuring Current
Buying a Multimeter
You can buy a basic multimeter for as cheap as $5. But this is something you are going to use for many years to come, I recommend spending a bit more on a better quality one.
- BSIDE ADM08A: http://bit.ly/2rDzPRL (Rich in Features and Affordable)
- INNOVA 3320: https://amzn.to/2VTY2mp (Cheap & Basic)
A DDM can be used to measure voltage, resistance and current. Modern multimeters even have many other advanced features, such as continuity test, diode test and measuring capacitance.
A basic multimeter has two probes and a dial in the middle for selecting which function to use.
There are usually 3 to 4 connectors to connect the probes depending on the function. The black probe is always in the black connector for ground. The red probe can go into one of the red connectors depending on what you are measuring.
Don’t be daunted by the amount of functions/modes that are available, we normally only ever use 4 or 5 of them. Here I will explain how to use these basic modes.
How to Test Continuity
Whenever someone ask you “have you checked your drone with a multimeter?”, they usually mean continuity check. This is probably the first thing you should know how to do with a multimeter because you will be using this all the time.
Continuity mode checks for short circuit between two points. If there is a short circuit the multimeter should beep. If the two probes touch directly, the multimeter should beep as the resistance is zero.
Before powering up your quadcopter for the first time, you should check for continuity between the positive and negative wires of the power lead.
It’s also useful for checking solder joints that looks sketchy, you can perform continuity checks to see if the pads are accidentally shorted together.
You can also use it to validate solder pads that are connected together on a flight controller.
Make sure your quad is powered off when doing continuity check. Sometimes the multimeter might beep for a split second then stop. That’s because there are capacitors between positive and negative. When you touch the pads with your probes, it charges the caps up so the meter thinks there is a short, but when the caps are charged the beep will stop. That’s normal and nothing to worry about, it should be fine if the meter doesn’t continue to beep.
- Check if the positive and negative of XT60 lead are shorted
- Making sure motor screws are not too long
- For finding solder pads that are connected on an FC, or which wire is which in a long harness
How to Measure DC Voltage
Before connecting power to a device, make sure polarity and voltage are correct. You can verify these with a multimeter.
Rotate the dial to select a voltage range that is higher than the voltage you are measuring. If you are not sure what voltage it’s going to be, start from the highest range and work your way down. By using the smallest possible voltage range, your reading will be more accurate.
If you get a negative sign, it means the probes are wrong way round. You can use this property to find out the positive and negative of a battery or power source too.
- Verify voltage
- Check for positive and negative
How to Measure Resistance
You rarely need to measure resistance, I mostly use it to confirm the value of a resistor when I am too lazy to look up the color codes.
Actually continuity mode is based on resistance measurement. If your DDM doesn’t have continuity mode, you can just measure the resistance instead. A short circuit has close to zero resistance.
Same as measuring voltage, you can start from a higher value, and work your way down if you don’t know what to expect. Using the smallest possible resistance range gives you better precision.
You can use a multimeter to determine how much current a component draws. To perform a current measurement, the probes should be connected in series with the device you are measuring.
There are usually two connectors on the DMM for current measurements – one for lower current (milli-amps and micro-amps), the other one for higher current (amps). Again, if you are not sure how much current you are measuring exactly, you should start with the higher range and work your way down.
Note that a multimeter is not designed to measure high current, typically not higher than 10 or 20 amps. Anything higher you should be using a power meter or a clamp meter instead.
With a DMM it’s okay to measure low amp draw devices such as VTX, FPV camera, or RX, but for anything that is power hungry, like motors, you should NOT use your multimeter or it might blow up the fuse.
A clamp meter (buy: http://bit.ly/2L7Q9t1) is a much easier way to measure high current. It allows you to take measurement instantaneously by clamping the jaws around a wire, which means you don’t need to break into the circuit to take measurement.
Get a Smoke Stoppers
A smoke stopper is another excellent tool to prevent “magic smoke” from your new builds. Use this between the quad and battery for powering up for the first time will prevent burning components due to build mistakes or faulty parts.