LEDs Give HP 3457A DDM’s LCD Display the Boot

Have you ever been so frustrated with a digital display that you wanted to rip the whole thing out and create a better one? That is exactly what [xi] did. Replacing their constantly used HP 3457A multimeter’s LCD display with a brighter LED one was a necessary project — and a stress reducing one at that.

While this digital multimeter is well-known for its reliability, its standard display is rather lacking. In fact, there are several mods already out there that simply add a backlight. However, as [xi] notes, LCD screens always have a certain angle where they still don’t quite show properly. So this hack reverses the LCD’s protocol and details the process of creating new LED display.

The issue of dim displays that comes with traditional digital multimeters is not a new one. One solution to this that we have seen before is a hack where someone decided to add a backlight onto their cheap multimeter. [Ken Kaarvik] got around the dimness altogether by giving his multimeter a wireless remote display of his choosing. It is interesting to see the different solutions that are made to the same nuisance. The first item on the agenda of [xi]’s hack was to successfully analyze the HP LCD protocol. With the aid of an ATmega32, the digits were decoded throughout the transmission frames.

Next on the list was to design a casing that would hold the LED display controlled by an ATmega162 with all of the corresponding parts sandwiched underneath. This was accomplished with three spiffy PCBs stacked on top of one another. After completed, a few discrete logic gates were added in the SPI hardware module when retrieving information from the HP to account for the 10-bit vs. 8-bit frames. But that was all the tweaking required!

This smooth build achieved an 80 Hz refresh rate that was faster than the original due to the increased speed of the CPU.  The power consumption was a bit higher than the previous version, but this was to be expected with the exceptionally brighter display — and well worth it at that.  What is your favorite multimeter display hack?

Thank you for the straightforward and beautiful hack, [xi].

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