LCD display problems only with Drok 5v/3A buck converter

I have been working on a Arduino GPS orchard project and now have a new problem…The unit works fine on 1) USB from computer 2) USB from cell phone battery 3) 9 volt siver energizery battery, but not from a Drok buck converter (12volt to 5volt 3Volt max). Installed the buck converter to use the 12 volt system on either a tractor or Kawasaki Mule to get away from using the cell phone battery and usb cable.

Here is a link to project that dev bailed me out on…

The hardware is:
Arduino R3 2560
Adafruit Ultimate GPS shield
Adafruit Standard LCD 20x4 Product 198 with i2C/SPI back pack
QGP waterproof 28dB Gain Antenna (Amazon)
Drok buck converter 12vot to 5 volt 3A (Amazon)

The display on the first three power sources is white on blue back ground (as it is supposed to be). With the buck converter/regulator the display is nearly invisible, faint and red in appearance. Turning the contrast adjuster on the i2C backpack doesn’t fix it. The contrast is all the way clockwise…any adjustment counter clockwise and there are no letters displayed.

I am electronically challenged and am one of those who doesn’t know a watt from an amp.

Is 5 volt at 3 amp too little power for my setup? Attached is my current version of my sketch and a picture of white display and “red letter” display.

Switching power sources solves the problem on either of the two units I have built.

Any and all suggestions gratefully accepted. Thanks

Feb_19th_odometer_1.0.ino (15.5 KB)

Please provide links to your actual hardware.
Google finds this Amazon item

Your "red letter" picture implies a different voltage on the LCD module. Measure it with a DMM.
The LCD will only manage a readable contrast with 4.5V to 5.5V. The LCD will "work" at 3.3V but the contrast pin needs a negative voltage.

I had never heard of a Drok. I suspect that it does not provide a reliable 5V at low currents. You are probably only drawing 50mA - 100mA. It might be happier with a heavier load current.


What is a DMM? Got it... Doh! Digital Multi Meter?

Here is the buck converter:

I will test the voltage put output...

Update...voltage reads 5.14 volts steady

Google DMM.

Adjust the contrast pot on the LCD. You should be able to get a good contrast with 5.14 volts. It is voltages lower than 4.5V that become diificult.

Use your DMM to read the total current at the 5V output. It would be interesting to see the current at the 12V input.


Edit. Looking at your link, the device is adjustable. So you could adjust it from 5.14V to 4.9V (or whatever your USB cable supplied). Then you only adjust the contrast pot once.

Making progress...besides learning what DMM stands for....

Voltage at barrel jack from Drok buck converter is a steady 5.14 volts, using my Fluke DMM...outside is supposed to be negative inside is positive right? Plugged in to Arduino the Drok buck converter supplies 3.83 volts at the back of i2c back pack as well as at 5V arduino plug and ground ??? Display no good.

Using cell phone battery Voltage on back of i2c back pack is 4.89 volts....output testing at 5V arduino plug and ground is also 4.89 volts display is perfect.

How am I losing the voltage from 5.14 at the barrel jack to 3.83 in the Arduino?

Any other diagnostic ideas?


More confusion…I eliminated the barrel jack and put the positive 5.14 volt wire into the vin socket and the ground wire into the grd socket on the Mega and viola!! it worked fine…Being a farmer and by nature a pragmatist, I don’t need to know why but barrel jack is culprit…got it out of a parts drawer, think it came from a bird scaring device we use, dimensions unknown… are these the correct size barrel plugs for my Mega? (2.1mm X 5.5mm)


First off. It is always worth posting a click-able link rather than a paste-able link. (12th icon from the left. looks like a piece of chain)

The photos in your Drok link do not show any adjustment but the comments say:

Yes the output voltage is adjustable via a adjustment screw and is variable at least 9-10 volts below input voltage.
By Randy on November 9, 2015
Small screw on bottom of unit to adjust voltage.
By Chuck M on November 9, 2015
the output voltage is determined by the amount of input voltage supplied. (within the variable range)
By Matt on November 9, 2015

You should always use soldered joints or professionally crimped connectors. Anything else is unreliable.

It is difficult to know how to reply to a Being a farmer and by nature a pragmatist
Most electrical connections just require "common sense"


David your last post didn't quite seem to be the whole picture so I continued Googling for more help.... apparently I wasn't the first to have this problem. The solution has to do with not being able to put 5 volts into the barrel jack as the Arduino over regulates it...I'll leave all the details to you Engineer types...

Solution is to take my 5.14 volts from the buck converter into the USB port and all is well. I did this and all works perfectly.

Here is a link to a previous thread on this forum that explains it all.

If that link doesn't is another pathway to it:

Arduino Forum > Using Arduino > Installation & Troubleshooting > output voltage is below 5V

Jump to post #8 by westfw (a fellow Californian!) for the short answer.

Thanks for your input now go have a cupa and a cracker.

Oops. You can put 7.5V into the barrel jack. Or 5V into the 5V pin. Or 5V into the USB connector.

Your Drok could be adjusted for an exact 5V or 4.9V or whatever you expect from your PC USB cable.
Or you could adjust it for 7.5V and go into the barrel jack.

My "guess" Drok had USB connectors.
Your "actual" Drok has bare wires.

Choose whichever style of connectors suit you the best e.g. Barrel or USB.

Arduino docs should explain your power supply options. If your current is modest, you could use the raw 14V from your tractor battery straight to the barrel jack. I do not advise it unless you have less than 100mA load.


Or you can put 5V into the INV, but not apparently into the barrel Jack...LOL

Thanks again...