Panel meter 5-30V DSN-DVM-568 three digits LED, Calibration tests ITTSB Blog

[Kiriakos GR]

Today I did set under the microscope of ITTSB Blog this Panel meter 5-30V DSN-DVM-568  three digits LED.

This is an item priced on eBay at best at $1.54 USD with 35 to 40 days shipping schedule.

Technically this is not an impressive item, in my tests it accuracy were found to be 2% that is way too much, this thing it is advertised as 1%.
This 2% error it is introduced in 95% of range, and you better take a good look of the pictures bellow.

Practically this meter with such terrible accuracy, this varying from 1.6% up to 2%,  this is not recommended as voltage monitor for lithium batteries.
My opinion this is that this meter it could have a good use only in vehicles using 12V or 24V, and nothing else.

Use of such a meter over a power supply, this is possible but it is not recommended if you care for precision work.

Speaking of wires ,  this meter supports three wires connectivity. 
R3 this is short component, this must be removed for three wires connectivity. 
As soon R3 this is removed, then VT contact point this now becomes Volt meter (Power supply input).
Volt meter consumption this is varying too,  sweet spot this is 6V / 10mA ,  above 12V consumption varying from 12~14mA.
Highest consumption recorded at Max 33V that is end of this meter measuring range, and consumption was  16.8mA
 

[Kiriakos GR]

Speaking of PCB of DSN-DVM-568, there is nothing special to it.

Beware: When this meter is in operation with 24V for five hours L78L05 Voltage Regulator (5V 100mA SOT-89 SMD) this run hot to 52 Celsius.
According to datasheet L78L05 SOT-89 SMD, Max operating temperature this is 125 Celsius.

[Kiriakos GR]

And now its time for a bit of hacking 

Warning the PCB it is tiny, do not attempt to engage with it, if you have a piss poor soldering iron or station.

This meter includes a resistor network with tiny solder points as jumper setting.
Unfortunately resistance value which it does influence the measurement this is at about 170K Ohm.
On-board resistors network this is three resistors, and unfortunately again .... default resistors values even as combined they are unable to create correct resistance value so resistor divider (circuit) to be adjusted with fine detail.

After experimenting, I did discover that in my meter by adding 172,3K Ohm resistance,  I did improve linearity and precision up to a level. 
 
Any improvement by adjustment in such meters this does not translate to better accuracy in full scale  0-33V.
Basically this meter as is  it does require power source at  6.5V,  so the circuitry to begin to operate correctly.
By assuming that your measuring range of high interest this is up to 20V, by fine tune of resistor divider, for example at 7V or 8V, you may expect good linearity up to 19V the most.

If your measuring voltage of interest this is 24V ?  Then you may tweak resistor divider accordingly, but beware that significant error will be introduced 14 Volts bellow that mark.

Last scenario this is the meter to be modified to operate with an 9V battery (or dedicated power supply), then you do tweak resistor divider for lower input voltage (example 2V), then good linearity will be up to 15V the most.

End of this chapter.