Tuesday, January 22, 2019

Working on improved fidelity of lights on DSKY substitute


Light dams, alternative production

I originally designed the light dams which separate the illuminated sections of the indicator and electroluminescent panels to be produced by 3D printing. However, the price and turnaround times were just too large. I redesigned these to be laser cut from black acrylic, using the laser cutting service, which sharply reduced both expense and turnaround time - under $30 with rush production and priority mail delivery.

Converting discrete LEDs into solid lit line on EL panel

I implemented the lines that light up between the three register numbers on the EL panel using 10 small LEDs on the PCB. The problem is that the result is a dashed rather than continuous line. I am going to experiment with fresnel lenses as a possible way to make a more realistic line.

As a backup I am looking at electroluminescent wire which I could install in place of the LEDs. That would require an inverter to produce the high voltage AC needed to illuminate the wire, and a method of switching it on and off based on the 14V switched AGC power.

I ordered a kit from CoolNeon that includes a power supply set to run on 9-12V, thus a simple zener diode from the switched AGC power supply (14V) will turn on the lines as long as the AGC is on and not in standby.

Converting two sides of minus sign to a continuous line

I had a similar problem with the signs. These were built with four LEDs arranged in a cross pattern, so that with the two side ones lit we see a minus sign and with all four illuminated a plus is seen. However, they are really four points while the real display has a continuous horizontal line for the minus portion of the sign.

I lasercut a light dam, with a line for the minus that bridged the two side LEDs. I hoped that with a diffuser on top, the minus sign would appear to be more like the real DSKY.
Shaping the light of the plus.minus sign LEDs
My first experiment put some diffuser paper over the light dam for the signs. I was fully satisfied with the improvement brought by this combination. I will glue the paper down to the light dam and then mount that dam on the PCB.
Light dam plus diffuser paper to blend minus sign line across full width
The second experiment was targeted at the row of LEDs that should appear as a solid line to the user, but are instead discrete spots of light when viewed directly. I tried the diffuser paper, but that didn't improve things much.

Next, I experimented with some inexpensive fresnel lens to see if I can get some stretching of the light between LEDs. As you can see from the image below, I was able to get some evening out of the light, but this is not a clear win.

Experimental 'smearing' of the LED output with fresnel lens sections
I may or may not continue working the fresnel lens, but there is still the electroluminescent wire I have on order that could provide an improved illuminated line with less work than cutting up and fitting bits of fresnel lens.


I came across an advertisement for a Kenbak 1 replica and decided to build the kit. This, like many such kits today, is an evocative rather than a literal replica. It looks similar but is smaller and mainly aims to recreate the experience of operating the front panel and running code. It joins my PiDP-8, Altairduino and similar such evocative replicas. In a sense, my DSKY substitute is also an evocative replica.

The kit comes with a small 3D printed case, a printed front panel, a PCB that attaches behind the front panel and all the components. It was well made and soldered together cleanly and easily. It makes use of an Atmel processor on the PCB rather than using an Arduino board like many other e-replicas.

The only problem I had upon checkout was with the tinyRTC module that was included with the kit. Something was defective on that board, causing it to fail to properly provide the real time clock or the nonvolatile memory. A real Kenbak did not have either, so this would have been an add-on aftermarket feature.

After plenty of debugging, I was certain that I had connectivity through to the chips on the TinyRTC board but it was giving errors when I snooped the I2C link it used. I bought a replacement RTC module from Amazon and quickly had the full functionality of the kit. www.adwaterandstir.com has the details of the uKenbak 1 kit, for those interested.

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