Hi,
This 7-segment LED display is fitted to a Chinese voltmeter-amperemeter (DSN-VC288 XK-001 V1.0). There are no markings. It has 9 pins. Does anyone have a link to its datasheet or know its part number?
Thank's
Have a look at this AliExpress sellers listing: https://www.aliexpress.com/item/33030667498.html, described as:
DC 0-100V 10A Digital Voltmeter Ammeter Dual Display Voltage Detector Current Meter Panel Amp Volt Gauge 0.28" Red Blue LED
Thanks, but I don't see the reference for the 2x3 digits display in this ad.
Oops, sorry! I misread your post and didn't realise that you were asking about the pinout of the actual LED display.
Maybe this will help:
(Found via 100V 10A DSN-VC288 DC Voltmeter Ammeter Review – calibration problems )
But it seems to have more pins than yours.....
Perhaps there is some form of intelligence built into the display. Are there any clues as to the driver chip or any indication of which pins may be power and ground - maybe thicker traces on the board?
In my opinion, finding the part number or data sheet for that particular piece is so unlikely that I would not spend my time looking.
I have made a LED tester with a resistor and a 9V battery terminal that I have used to find the pin-out of LED displays. The resistor value is high enough to limit the current of most LEDs down to about 1mA with a fresh Alkaline battery, but I don’t have the specific value handy. The resistor is soldered to the positive lead and heat shrink covers that connection. Just a little bit of the other side of the resistor is exposed to use as a probe. The negative lead was soldered to a scrap of resistor lead and heat-shrinked to make it probe well also.
To figure out a display, I hold one lead on pin 1 and then touch all of the other pins with the other lead. If an LED lights, I write down the pins, polarity, and segment. Then, I move the held lead to pin 2 and repeat. I keep doing this until I have written down the pins for every segment. If you are lucky, you will start with the correct battery polarity; if not, you test all of the pins one way without any light and then start again with the correct polarity.
I was expecting to receive the classic model, but my Chinese friends played a joke on me.
I don't want to try testing the segments with a battery and a resistor, as the operation doesn't seem to be that simple. None of the 9 pins receives a fixed voltage or is connected to ground, there are signals on all of them.
There is no driver, everything is managed by the MCU in bit bang mode.
What's certain is that it's not managed by SPI or I2C.
I'm going to install the display on a breadboard, and make wire connections by interposing DIL switches to try and understand.
With only 9 pins to drive 48 segments, it may be Charlieplexed.
This could also indicate Charlieplexing.
As there is no embedded intelligence in the display (no pins to power a circuit), the Charlieplexed solution is the most plausible.
I agree with this approach, but you must still use current limiting resistor(s) to avoid damaging the display. 330R should be ok.
Your DIL switches will probably be only SPST. If the display is Charlieplexed as we suspect, you will need some SPDT switches with centre-off position for testing, so that for each switch, it can be connected to both 5V and ground, and it's COM pin connected to the display pin using a resistor.
After testing, I can confirm that the display is Charlieplexed. What's more, this model has no ammeter calibration facility, and the measurement is not very good.
So be very careful with photos when ordering, or open a dispute if they are misleading.