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$1 DVM as a Digital Input Display — Parallax Forums

$1 DVM as a Digital Input Display

My 5V circuit has a potentiometer to adjust a timing delay and I wanted to add a digital display for precise calibration. I realized that 0-5 seconds could be displayed as 0-5 volts on a dollar DVM, so I just used the pot as a 5V voltage divider and connected the DVM to the wiper. (This requires a 3-wire DVM, since a 2-wire unit won't work below ~3V.) Micro reads the voltage via ADC and the code converts into seconds.

If desired, the input range could be limited or shifted by adding one or more fixed resistor(s) in series with the potentiometer. This would also reduce the sensitivity of the pot adjustment and help stabilize that last flickering digit on the DVM. I used a $1 Powerbank for my 5V supply. One advantage to leaving the upper limit at 5V is that I can use the DVM & pot to check for full 5.0 V output. Less than 5V indicates a low 18650 battery in the Powerbank and time to recharge.


  • WhitWhit Posts: 4,183

    Nice work erco!

  • @Whit said:
    Nice work erco!

    What he said. Nice work. Let's see. the powerbank was from your local dollar store? But who supplied the display?

  • ercoerco Posts: 20,013
    edited 2021-10-12 03:05

    All pre-Covid Ebay $1 purchases. Most of erco's dollar deals are gone now. Even if you can find something for a buck today, Chinese Ebay sellers want $3-4 for shipping. :( Ken may be happy but erco is not! I am buying more on AliExpress now that they take Paypal. The best deals are buying multiple units to find a good deal on bulk shipping. Now I'm even MORE of a hoarder!

    For instance... I got 4 of these green DVMs for $4.96 (incl tax & shipping). But ordering a 5th unit, the shipping jumps $2. It's a game...

    Another: Free ship on ONE FM radio kit, but two will cost $2.33 to ship. So order individually!

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