Here’s a modification that I have been meaning to do for a while. It involved replacing the PCB in one of my power supplies with a modified version designed by me that upgraded the size of the 7-segment LED display.
I ordered the board from OSHPark. My experience with them has been positive; the turn around time was about 2 weeks and the gold finish is very nice. I’m fine with the colour of the solder mask, however note that the mask is a matte finish rather than the typical “pearl” or “glossy” finish that I am accustomed to seeing on PCBs. Not a big deal, but something to think about. Also, the traces are a bit difficult to see through the solder mask.
I of course did not fully check my notes when throwing together the schematic for this project which resulted in the boards I received having the ‘a’ and ‘g’ segments reversed. A few cut traces and a jumper wires later and all was working as expected.
I originally tried to think of a better way of re-attaching the new display board to the existing display measurement/logic board, but in the end the simplest solution won out and I just re-soldered the new display board back. The header pitch is 3.81mm and was a total pain to find (yay eBay!).
The end result is a bright, clear and LARGER display. Here I have contrasted it with the model right after the 6050C, the 6050D which has a larger digital display (and also does not display the measurement mode as the 6050C does, E or I).If I decide to pick up any more of these supplies, I think I’d make the same display modification to them as well. I have been looking at the 6050A models (which can usually be had for cheaper): these might also be good for a “digital makeover” involving removing the analog meter and designing a new digital display PCB.
In keeping with the theme of back-light mods, I have another one here for you all. Recently I was able to get my hands on a well-loved (read: had the piss kicked out of it) Tektronix DMM 916. The specs are nice:
- 4.75 digits
- 40,000 count
- Basic DC accuracy of 0.06%+1 count
The only problem which I didn’t know until I got the meter in my hands was that the back light was horrible:
Wait, where is that back-light?
Still can’t see it? Turn off the lights!
I’m not sure if this is “factory standard” or just a sign of the age of the unit, but either way it needed some change. The first thing I did was to open up the meter and check out the display:
There is a small slot on one side of the display assembly where the lamp bulb pokes into the light pipe. At first I thought I might use a standard through-hole LED, but realized that I wouldn’t be able to mount it without either cutting the trace (for the limiting resistor) or cutting the display. I didn’t want to mod the board, in case I or someone else wanted to restore it back to a incandescent bulb. So I choose to use a SMD chip LED and resistor, and build it “tee-pee” style on the top of the display PCB, so that the LED and resistor would stick up vertically into the display light-pipe recess:
The LED is blue, Digikey part number 475-2816-1-ND with a 270ohm current limit resistor. The bulb sank about 20mA while the LED uses ~18mA, so a bit more efficient. I’m still not sure about the blue, but I figured it matches the theme of the case, so why not:
And as is evident, it is much brighter even with the lab lights on. Curiously, it is not much more legible in the dark in terms of the digits on the screen as I would have thought.
Just a quickie here to show you what I’m working on currently. Thanks to Eric, I now have a I2C/SPI/8080/6800 compatible monochrome OLED display! This is just a test to make sure the display works and that I got the correct pin-out for the SPI interface: