Hello everybody!
I going to do power off mod and backlit mod (with permanent light, not original). And I want that light will be off after DMM going to sleep. Can I connect +V of the LEDs to the positive side of C33, like for the IR transistor?
And should I add driving the backlight leds with transistors like in UT60E schematic?
Hi,
I don't think I would use positive side of C33 for the anode of the LED backlight. According to ES51922 datasheet pin 1 and 2 (C33+) is the output of on-chip DC-DC converter and we don't know how much current that can supply. I would probably use VC+ (C36+ 10uF) for the backlight anode.
For switching the backlight on/off I think you have a couple of options.
1. If you want the backlight on all the time except during sleep you could probably use pin 58 "SLEEP". Datasheet says "asserts low in SLEEP mode" so you could probably connect to the base of a NPN transistor to this pin58 (with a base resistor) and use the collector to drive the cathode of the backlight (with dropping resistor).
2. There is a backlight enable output on the ES1922, pin105 "BKOUT". ES1922 datasheet says "this pin will change from -3V to +3V for 60sec once press BKLIT". So then you need a switch (use hold switch?) on the "BKLIT" pin102 to pulse it low. Looks like you can change the time from 60sec to 180sec using "BKSEL" pin113. So you could connect the base of a NPN transistor to this pin105 and use the collector to drive the cathode of the backlight (with dropping resistor).
BTW, I was stupid enough to insert a 9V battery reverse polarity to my UT61E and left it on for a while without checking it. It took out the tant C36 from reverse polarity and blew a hole in the regulator W1, 7201U30. I replaced the 10uF Tant and the regulator with a MCP1703T (cause that's what I could get in the same package from element14). All working again now so I'm glad it didn't take out the main controller IC.
Regards, Dean.
Disclaimer, I have not tried any backlight mods so can't say for sure if either of the above mods work. I see there are other mods for UT61E backlight online, I haven't looked at them in detail so there could be better ideas there.