Hacking Hobby King Volt Meter

Hacking the Hobby King RC 3 Digit Volt Meter To read below 3.2 Volts
Hobby King has a cheap (Less than $3.00) volt meter designed to be installed in RC cars, planes etc to monitor the battery voltage.
Hobby King Volt Meter The range on these meters is 3.2 to 30 Volts DC

They are very popular with the RC crowd and are out of stock all the time. They ship from Hong Kong and take 2-3 weeks to receive. If you order 10 of them shipping is only $2.99 so they are not a bad deal.

I wanted to add these to some small adjustable power supplies that I have that do not have a volt meter built in. But I wanted to read voltages lower than 3.2 volts. The 3.2 volt limit is due to the 7130-1 3 volt low drop out voltage regulator. So I started looking at ways to power this from a source other than the voltage source that is being measured by the meter. I cut the trace of the inout to the 7130-1 voltage regulator and in this example I powered it from a 9 volt battery. When this is installed in my adjustable power supply I will power it from the 5 volt fixed voltage in the supply.

Steps to duplicate

  1. Cut the trace leasing to the 7130-1 voltage regulator on the top of the circuit board. The trace is on the lower right of the board and goes from a set of small pads and travels back around the capacitor. I cut it with a hobby knife. Sorry for the bad photo Check your work with a volt meter from the + Battery input to the input of the voltage regulator to make sure you cut all the way through the trace.


2 Solder your new supply wires to the top of the regulator on the back of the board and ground.
Be careful when you solder onto the voltage regulator it does not take much heat to loosen the whole regulator from the board.
The new wires are the two soldered to the left in the photo.

Power the board up with your external battery and it should read 0 volts. If it reads the voltage of the battery you did not get the trace on the front of the board cut all the way through.



The meter works good and tracks with by multimeter just fine for anything over .5 volts. Under this it does not always see the change in voltage if I increase the voltage of the power supply. It does seem to read better at under .5 volts if it is reading a decreasing voltage.
There is a small pot on the back of the meter that allows you to calibrate the voltage display.

You Tube Video of modified meter in action.

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