15 March 2016

Four digit display with HP 5082-7300

Arduino Nano counting...
My interest for old display technologies got a bit of satisfaction when I lighted up a bunch of HP 5082-7300 chips. These are 8 pin displays with an integrated BCD decoder (0-9, dash, blank) plus RHS decimal point that emulate a dot matrix configuration. The required power supply is 5 V and today they can be easily driven with the microcontroller of your choice. The integrated logic includes a latch, so you can connect more displays in parallel and multiplex data through the [Latch Enable] control.

One remark not clear from the datasheet: the decimal point is latched as well as ABCD inputs.

My first application is a simple 0000 to 9999 endless counter. It is a good way to test all dots work, measure current consumption and do other optimizations.

As expected, these little displays produce a good amount of heat. According to the datasheet, at 5 V the current drawn is well above 100 mA, so that's more than 0.5 W of heat to dissipate. To minimize the risk of failure due to heat I mounted my 5082-7300 on a "socket", so I can add a small fan on the side if I want to.

Then I tried to reduce the voltage supply, both to the Arduino and to the display string. The good news is that there is no change in dot luminosity down to 4.1 V and the average current goes down to 60-70 mA per display: that's about 0.25-0.3 W dissipation per display. Cool, isn't it?

Click to zoom and see the logic through the red plastic. Last digit was changing from 6 to 7.
Voltage supply can be further decreased but then pixel luminosity is not uniform anymore.

So, in the final application I can run the whole setup Arduino+HP 5082-7300 at 4.2 V or so. Given the amount of power needed by the display rack itself it makes no sense to optimize the firmware for a lower consumption or use a stand-alone microcontroller in place of an Arduino.

Now it is time to fill the perfboard with a Nano, an RTC and some form of alarm function. And write some code, of course.

I have some HP 5082-7300 spares in case you land on this post looking for this specific part.