These are interesting little meters. I found it a little amusing that you choose the one that was pretty well spot on accurate to pull apart :). Thanks for the tear down.
Nice AvE reference. Funny, 'cos is shouted it at my screen just before it popped up, haha. Great tear down. Simple devices but nice to see how it works!
They use the same IC to do DC, just using normally a TL431 as a 2V5 reference voltage and supply. Easy enough to separate the AC input pin from the measuring, and then improve things by changing the zener to a TL431 to give a constant voltage supply, and get better accuracy, though you will need to improve the capacitive dropper as well. The DC versions use the series resistor and TL431, though often they omit the capacitor for filtering, or use a mystery somewhere around 100n to 470n chip ceramic instead, and for those the voltage calibration can be a little spotty, though you can easily enough calculate the correct values for the divider and solder in the appropriate resistors somewhere. Just bought some as well, panel mount in a rectangular cutout, with a range of 5-20V, which are not too bad accuracy wise, all reading within 3 digits of each other. Just note they are not reverse voltage protected, as they use the little micro body diode as protection, which kills it.
Awesome video, thanks for sharing. I was thinking about reusing these indicators as a drop in replacement for embedded projects where AC voltage measurements are needed but the amount of work required to reverse engineer the multiplexing of the LEDs seems to be quite significant. Have you managed to do it?
Good video POS, now these panel meters have the appearance of a high end industrial control but obviously not. A bread board component test would have been interesting. I found your theory a bit confusing.
Great stuff. Shalom, I'm trying to modify this circuit to use for high voltage DC measurement, 110 - 150V, i reckon replacing the 470nF cap with a 5k Ohm might just do it! EDIT: It worked! However, it works similar to when one measures dc voltage on the ac side of a basic multimeter like the DT-830D (info that may help you narrow down what chip it uses) the readings are 2 times the actual value. i.e. 19v dc is read as 38v on the LED display, precisely. The device was indeed designed to measure 50/60 Hz ac after all. Works for me though, since all i need to do is immediately half down the reading mentally. That said, i think 250v dc is the highest one can measure with this modification, since the LED is designed to show around 500v max. EDIT: Scrap 5k Ohm, 15k - 20k Ohm works well for dc, 5k Ohm causes the 16v capacitor to start burning due to over voltage.
Not great for use on a Variac since the circuit drops out as voltage gets lower. It's have to be modified to have independent power supply (off incoming mains, before Variac) then have the voltage measurement tapped off after the Variac.
where the 50/ohms resistor's leg is soldered? becoz i have this device without 50/ohms resistor, kindly let me know the correct pinout of this resistor.
I would not change the the power supply components. What you can do is to use a potentiometer in the voltage divider chain to pin 9. So you can adjust the meter to get a more accurate display of the voltage (at least at a fixed voltage say 120V or so). BTW for just a little bit more money you can also buy the same type of meter that also measures current (using a pick up coil).
There is a HEAP of non-isolated mains voltage in that thing. The resistors are technically all copping full mains voltage, with only the load to pull them down. So a potentiometer might just crap out under those conditions. I dunno, I don't really think his reverse engineering is correct anyway.
@@johncoops6897 Next time i'll put a warning/claimer in my comments!!! Of course everything is connected to the mains. Of course i have not done any re-reversed engineering. But what is it that you think is wrong?
@@johncoops6897 Any potentiometer should be fine as long as you respect its voltage ratings. If you don't know the voltage rating it's surely good to at least 30v (assuming that's within its power limit). As the first part of the voltage divider is a high value 470k there shouldn't be too much voltage on the smaller two.
These are interesting little meters. I found it a little amusing that you choose the one that was pretty well spot on accurate to pull apart :).
Thanks for the tear down.
Great observation :) I think it would be fun to know what part(s) is/are out of spec to throw the thing off.
Capacitor: 474 means 47 plus four zeros in picofarad. So it is 470000 pF equals 470 nF.
I always look forward to your videos, and the choice of beer. You're such a great teacher!
Nice AvE reference. Funny, 'cos is shouted it at my screen just before it popped up, haha. Great tear down. Simple devices but nice to see how it works!
They use the same IC to do DC, just using normally a TL431 as a 2V5 reference voltage and supply. Easy enough to separate the AC input pin from the measuring, and then improve things by changing the zener to a TL431 to give a constant voltage supply, and get better accuracy, though you will need to improve the capacitive dropper as well.
The DC versions use the series resistor and TL431, though often they omit the capacitor for filtering, or use a mystery somewhere around 100n to 470n chip ceramic instead, and for those the voltage calibration can be a little spotty, though you can easily enough calculate the correct values for the divider and solder in the appropriate resistors somewhere. Just bought some as well, panel mount in a rectangular cutout, with a range of 5-20V, which are not too bad accuracy wise, all reading within 3 digits of each other. Just note they are not reverse voltage protected, as they use the little micro body diode as protection, which kills it.
The voltage divider would be the pin measuring the voltage. The other would simply be powering the IC.
So how to make it more accurate would be the next question
Awesome video, thanks for sharing. I was thinking about reusing these indicators as a drop in replacement for embedded projects where AC voltage measurements are needed but the amount of work required to reverse engineer the multiplexing of the LEDs seems to be quite significant. Have you managed to do it?
The LEDs are controlled using Charlieplexing. Here's a video I did about that topic: th-cam.com/video/OYDD5BWz2Ms/w-d-xo.html
Good video POS, now these panel meters have the appearance of a high end industrial control but obviously not. A bread board component test would have been interesting. I found your theory a bit confusing.
Great stuff. Shalom, I'm trying to modify this circuit to use for high voltage DC measurement, 110 - 150V, i reckon replacing the 470nF cap with a 5k Ohm might just do it!
EDIT: It worked! However,
it works similar to when one measures dc voltage on the ac side of a basic multimeter like the DT-830D (info that may help you narrow down what chip it uses)
the readings are 2 times the actual value. i.e. 19v dc is read as 38v on the LED display, precisely.
The device was indeed designed to measure 50/60 Hz ac after all.
Works for me though, since all i need to do is immediately half down the reading mentally.
That said, i think 250v dc is the highest one can measure with this modification, since the LED is designed to show around 500v max.
EDIT: Scrap 5k Ohm, 15k - 20k Ohm works well for dc, 5k Ohm causes the 16v capacitor to start burning due to over voltage.
Perhaps it's best meant for metering a Variac output (if it were a little more accurate)
Not great for use on a Variac since the circuit drops out as voltage gets lower. It's have to be modified to have independent power supply (off incoming mains, before Variac) then have the voltage measurement tapped off after the Variac.
@@johncoops6897 Agreed - I figured there would be a bit of hacking to give that meter a separate supply - but that's the fun part.
Interesting, as always, thank you.
Did you pull apart the Yellow one?
Wasn't that the most accurate one?
It went back together easily.
where the 50/ohms resistor's leg is soldered? becoz i have this device without 50/ohms resistor, kindly let me know the correct pinout of this resistor.
Interesting video. Thanks!
I would not change the the power supply components. What you can do is to use a potentiometer in the voltage divider chain to pin 9. So you can adjust the meter to get a more accurate display of the voltage (at least at a fixed voltage say 120V or so). BTW for just a little bit more money you can also buy the same type of meter that also measures current (using a pick up coil).
There is a HEAP of non-isolated mains voltage in that thing. The resistors are technically all copping full mains voltage, with only the load to pull them down. So a potentiometer might just crap out under those conditions. I dunno, I don't really think his reverse engineering is correct anyway.
@@johncoops6897 Next time i'll put a warning/claimer in my comments!!! Of course everything is connected to the mains. Of course i have not done any re-reversed engineering. But what is it that you think is wrong?
@@johncoops6897 Any potentiometer should be fine as long as you respect its voltage ratings. If you don't know the voltage rating it's surely good to at least 30v (assuming that's within its power limit). As the first part of the voltage divider is a high value 470k there shouldn't be too much voltage on the smaller two.
They're just way over designed power on indicators.
I suppose if you have widely variable voltage from your power provider they could be useful.
But they're not really going to work for my application.
where is the dead cat? we all know that curiosity killed the cat. Did it try and drink your beer ;-)
"Satisfaction brought it back."
I like where this is going HAHAHA
It shows how cheaply these are made when they don't agree on the same supply voltage. LOL.
You buy them by the dozen, they spend more time on the looks of a quality component than the circuitry inside.
Precision resistors for the divider chain would probably double the price.