0,36",5 Digit DC 0-33.000V Digital Voltmeter Panel Meter  - Page 1
Forum section: electronics / projects

author: 0xFFF0
author_rank: Regular Contributor
timestamp: May 10, 2024, 02:38:05 pm
content: 0,36" 5 Digit DC 0-33.000V Digital Voltmeter Panel Meterhttps://www.ebay.de/itm/132474589055Does anyone know if you can change the voltage divider? Found two resistors: 330k and 20k. The division ratio is a bit strange.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 10, 2024, 03:00:50 pm
content: not sure if the firmware in them is settled as a maximum of 33volts ... even if you change the divider you may get stuckyou have the 3 1/2 digits with intersil 7106 or 7107 lcd or led display 1,999 19.99, 199.9you have the 4 1/2 digits based on intersil 7135 ddm chipsets, you can change the decimal point and add a divider ....they display 1,9999, 19.999 199.99 .....around 20 usd when i've bought them ... be careful, you have fakes on ALI .... it's a dip ic not a surface mount in the picture(s)smd do existbut the most i've seen are based on some (top sanded / unknown) mcu's

author: 0xFFF0
author_rank: Regular Contributor
timestamp: May 10, 2024, 04:15:30 pm
content: All these modules are ST MCU based.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 10, 2024, 04:27:14 pm
content: not all of them if you search and choose wisely ...took me a while to find the 4 1/2 ones with real dmm ic'shttps://www.china-purchaser.com/goods/item/detail/id/21678871866https://www.china-purchaser.com/goods/item/detail/id/21678871866or build your self one with arduino like this :https://www.digikey.com/en/maker/projects/how-to-make-a-simple-digital-voltmeter-with-an-arduino/082dff9d725549aea8bf84a7e302c1b2and you can adjust the range to your needs ... an arduino mini / pro etc ... well placed behind an 16x1 lcd or serial led display etc..

author: Kleinstein
author_rank: Super Contributor
timestamp: May 10, 2024, 05:06:55 pm
content: There could be other similar modules for different ranges. It would need a change in the divider and the code / cal constants to really show the right result.AFAIK many of those modules use a MCP3421 ADC with internal ref. and a STM8 µC.Without an extra buffer it is tricky to use a 10 M divider like with most DMMs. The lower resistance is still OK for power supplies and similar projects.

author: floobydust
author_rank: Super Contributor
timestamp: May 10, 2024, 05:08:23 pm
content: There are a few different varieties of these 5 digit panel meters. Usually using either of two types of ADC, check which one you have.I dislike the sluggish averaging firmware they use to cover up all other cheapness.

author: 0xFFF0
author_rank: Regular Contributor
timestamp: May 10, 2024, 05:39:36 pm
content: Quote from: Kleinstein on May 10, 2024, 05:06:55 pmAs a matter of fact. It's an MCP3421. Unfortunately, the differential input Vin- has been connected to digital ground. R1=330k, R2=20k, full range 30.000 equals to 1.7142V

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 10, 2024, 06:55:51 pm
content: Quote from: 0xFFF0 on May 10, 2024, 02:38:05 pmYes, you can add several MOhms in series with an input to get e.g. 330.00 V limit. I have done it, just not remember exact additional resistance value at the moment.And I cut wire and added additional mosfet (2n7000) to move a decimal point.

author: mariush
author_rank: Super Contributor
timestamp: May 10, 2024, 07:13:07 pm
content: Either way, you're limited by the linear regulator used, with maximum voltage of 35vThe one in the ebay link uses MST5333B ... datasheet attached.The resistors make sense if they use that microchip adc with 2.048v reference.If you want higher voltage, either change the linear regulator or replace with a switching (buck) regulator and separate from the adc input / voltage divider

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 11, 2024, 06:21:25 am
content: Quote from: mariush on May 10, 2024, 07:13:07 pmThose precision voltmeters usually have separate power input, so power supply voltage range is not connected with measured voltage.