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Replacing OLED screen on an Agilent U1253A Multimeter

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--Oz--:
Its semi easy to copy hardware (relatively), the FW is Agilent's secrete sauce, and to debug FW that cant be read out of the mpu is pretty tough. I agree, sure would be the cleanest way.

gamalot:
Hacking the firmware looks like a good idea, but when there is an MCU or FPGA on the replacement display, the customized splash screen is very simple, and even some tricks can be made.

One of the features in my current implementation is that it can show a different splash screen every time you power up or wake up the meter (sequentially or randomly).

gamalot:
Aside from those icing on the cake features, I think the most important thing I discovered and solved was why the MCU reads from the OLED display's RAM.

I've noticed that some readings only happen when the battery's voltage drops below a certain threshold (on my U1253B it's around 8.3V), and if the read back data is not what it expects, it shuts down immediately.

I'm not sure if the same thing happens with the U1273A as I don't have one. If you happen to have one and replaced the display module with one which has an MCU or FPGA, you can verify if it works at low battery voltages (my implementation works down to 6.2V)

AVGresponding:

--- Quote from: gamalot on December 11, 2022, 07:57:29 am ---Aside from those icing on the cake features, I think the most important thing I discovered and solved was why the MCU reads from the OLED display's RAM.

I've noticed that some readings only happen when the battery's voltage drops below a certain threshold (on my U1253B it's around 8.3V), and if the read back data is not what it expects, it shuts down immediately.

I'm not sure if the same thing happens with the U1273A as I don't have one. If you happen to have one and replaced the display module with one which has an MCU or FPGA, you can verify if it works at low battery voltages (my implementation works down to 6.2V)

--- End quote ---

I have such a 1273A. I shall investigate.



At 6.0V (this meter uses 4x AAA) the meter pulls 26mA, absolute madness... the first battery warning, an "x" in the battery icon, comes on at around 4.6V, and it's using 32mA. The "Change Battery" text comes on at 4.25V, and the meter shuts down after a few seconds. It will power back up by pressing a button, but shuts off again quite quickly. The current draw at 4.25V is 36mA.

gamalot:

--- Quote from: AVGresponding on December 11, 2022, 12:01:31 pm ---
--- Quote from: gamalot on December 11, 2022, 07:57:29 am ---Aside from those icing on the cake features, I think the most important thing I discovered and solved was why the MCU reads from the OLED display's RAM.

I've noticed that some readings only happen when the battery's voltage drops below a certain threshold (on my U1253B it's around 8.3V), and if the read back data is not what it expects, it shuts down immediately.

I'm not sure if the same thing happens with the U1273A as I don't have one. If you happen to have one and replaced the display module with one which has an MCU or FPGA, you can verify if it works at low battery voltages (my implementation works down to 6.2V)

--- End quote ---

I have such a 1273A. I shall investigate.



At 6.0V (this meter uses 4x AAA) the meter pulls 26mA, absolute madness... the first battery warning, an "x" in the battery icon, comes on at around 4.6V, and it's using 32mA. The "Change Battery" text comes on at 4.25V, and the meter shuts down after a few seconds. It will power back up by pressing a button, but shuts off again quite quickly. The current draw at 4.25V is 36mA.

--- End quote ---

Thanks for your testing work. It looks like your replacement display works fine at low voltage, maybe it's because the U1273 doesn't really care about the data read back from display, or the guy who made the replacement took care of that in the FPGA.

I know that the U1273 is a newer design, using low power devices, and the lower current is to be expected. But considering that most of the power consumption is on the OLED, your test results really shocked me!

For comparison, I made separate power connections for my display module and it draws 20mA at 6V and 27mA at 4.25V.

---

Sorry I made a stupid mistake! The test results above were measured with the brightness set to low. I measured 33mA at 6V and 47mA at 4.25V with the brightness set to high.

If your results are also with the brightness set to high, then there is a big problem with my design.  :(

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