Multimeter backlight modification

[adras]

Hello,

I've got a multimeter which is based on FS9922. Unfortunatelly that thing has a horrible backlight control. It turns off after 10 seconds which makes it quite useless.

I'm now wondering how I can modify it that the backlight is always turned on. Switching it would be cool, but I think the most easy way is to just have it always on when the multimeter is on as well.

There's one interesting pin, LBOUT. My question is now, is it a good idea to connect that pin to VDDA? Or in general, how can I achieve that the backlight is always on when the multimeter is turned on?

I hope you can help me

[TheElectricChicken]

sounds easy enough, the link is not working though

[adras]

Link fixed, you can now see the datasheet there

[Rostislav]

hi!

button set with fixing for illumination. such as, eg: http://www.chipdip.ru/product/ps700l/

ps. can you have schematic your multimeter?

[Jay_Diddy_B]

Hi,

No need to modify the DMM, press the 'HOLD' button for more than 2 seconds.

The datasheets says:



Regards,

Jay_Diddy_B

[mariush]

Jay, the backlight will turn off after 10 seconds no matter what, it's built into the chip.

To answer op's question, see the example circuit in the datasheet, you could hook a wire before the LED and after pressing HOLD for two seconds, the chip will send power through wire which you can detect with a microcontroller or some other chip (some kind of on/off switch etc which will only turn off when the meter is powered off).

[onlooker]

Other than try to power the LED directly from VDDA as mentioned, VDD can also be used if OP is willing to replace the LED with a non-white one.

[adras]

Turned out that the pin goes HIGH to +3V. The actual voltage for the backlight panel is 6V so there's some boost circuit between the pins. I just searched for a pin which is always +3V and connected it to the backlight output pin.

Now the display is always on, when the multimeter is powered.

Thanks for your suggestions.