Yep - that's why I was checking, as the OP gave the impression that the board just had the LEDs, main IC, and a couple of voltage regulators. I'm surprised* that it doesn't have any resistors between the segments and the control chip's outputs, and perhaps a trio of transistors used for multiplexing.
cheers
Jules
It could even be a PIC type processor but that might be too costly even if a masked programmed version. Only bonus for a high volume chip would be things like brightness control would be included.
Bob
Like this one?
measure their own power supply.
I was thinking more of the kit that can allegedly be supplied via that page, which can. Although, if an extra component can be tolerated, an isolating DC-DC converter for the DVM supply isn't expensive.
That is usually a matter of a little analogue circuitry
Easier to simply buy one which can. There's a big range out there in the more usual display sizes. In my case, the requirement was for a much smaller one than you'd probably want for other uses. And luckily is designed for the job I wanted it for.
Two resistors fixes that.
So the problem is electrically dimming it yes?
And you don't know how the backlighter is driven?
Ive forgotten..was it LED or LCD?
It might or might not do. For such a device to measure voltages lower than its supply would require it to have an SMPS, etc. Mine stops working at about 7 volts. Which is fine for a 12 volt battery, but may not be for other uses. One which has an independant supply can usually measure from zero upwards.
I've got a couple of spec sheets for this sort of meter - and none of them give a simple mod for measuring their own PS.
Yes.
It's LED. There is no LCD backlit unit of this small size available that I could find - despite exhaustive searching.
It's LED.
There would be no real need to switch off a backlight during the day.
so a segment type display.. any idea whether they are common anode, or cathode?
and whether is statically driven, or multiplexed?
if its relatively static a hack (literally to the PCB) like this might work
It could, but if it were something like that, wouldn't there be resistors between the LED segments and the PIC's I/O lines? I'm not sure if any PIC (at least anything small/cheap enough for this board) would have enough I/O lines for direct segment drive, so there'd be some kind of multiplexing (and therefore a handful of other components) on the PCB.
Makes me think this control IC is a custom 'blob', or there are some additional components present that Dave hasn't mentioned.
Maybe it's possible to cut the PCB traces between the LED display and the IC, and switch in other resistors under transistor control - but I realise that's not very elegant as it'd need quite a few components :-)
cheers
Jules
IF the display is not muxed, but demuxed with some sort of static latch/current driver, then usually there is a common anode or cathode line linking all the display units, that goes either to ground or Vcc, that can be cut and have a chopper circuit inserted to dim them ..
Since continuosly variable dimming is NOT required, that can be relativeley simple.
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