megi's PinePhone Development Log RSS

2022–03–31: Keyboard light

Pinephone keyboard is hard to use in the dark. Easy usage in the dark is one of the benefits of on screen keyboards, apparently. With one usless Type-C port on the Pinephone that shouldn't be used for charging or USB peripherals, because of risk of damage, there's an opportunity to improve this.

I've bought a Type-C connector that is meant for home made Type-C power sources. It has resistors configured on CC pins, so that the device it's plugged into thinks the connector is part of a power supply. This is pretty good, because this connector will not risk damaging the phone or the keyboard charger when connected to the phone that is currently inserted into the keyboard.

I bought this connector to solder a LED/resistor to, so that I can have a compact LED light oriented towards the keyboard when necessary. The LED will be supplied by the keyboard battery.

What I needed was the above linked connector, a 220 Ohm resistor, a white LED unsoldered from a 12V LED strip (I measured it and it has a V-I characteristic knee at around 2.6V in forward direction, and gives enough light at about 7–10mA), UV epoxy, and a star or other more portable source of UV radiation. Some common tooling to put it all together is necessary, too.

I soldered the LED and the resistor to the connector. I tried to solder it in such a way so that LED will face the keyboard when the plug is inserted into the phone:

Other angle:

Then I added the epoxy, to make the connector more durable, and to unexpose the metalic contacts on the PCB. I pushed the epoxy with a syringe and a needle under the resistor and the LED, and all over the PCB:

A 5 minutes of exposure to UV radiation hardens the epoxy:

The benefits of this kind of epoxy are that it hardens quickly, and doesn't change shape/volume during hardening.

And the other side:

Exposure again:

And… done: :)

This is how it looks inserted into the phone:

The first test in dark conditions:

As expected, the LED light will need some shade, or a mirror to make it not shine right into my face. I've added a bit of a isolation tape for a test:

It's still a bit translucent, but good enough for making a quick video:

And the keyboard use in dark is much easier now. :)

I'll have to figure out a better shading, maybe something that will reflect the light towards the keyboard, instead of wastefully absorbing it.

Power consumption of this is ~60mW. This adds ~4% to original Pinephone power consumption and 2.5% to Pinephone Pro power consumption when in active use.

The LED is turned on only when the keyboard power is enabled with the keyboard power button, so it also serves as an indication when the keyboard power output is on.