Arne's Electronics Series

Larson Scanner & Beyond

The Larson Scanner was thus named decades after its appearance on BSG and Knight Rider. It's the effect of a red light, or "Cylon eye" bouncing side to side, seemingly scanning. It's easy light up LEDs one at a time going in one direction using a 4017, but the bounce requires extra logic. It's of course trivial using a microcontroller nowadays, but back in the '80s 7400 and 4000 series had to be used. I found a schematic made in 1983 but didn't have the 74193 in my bins. Curious, I set out to see if I could solve the problem using what I do have.

2020 edit: I built it on a breadboard and it works, aside from the 74HC138 outputs being Active Low (opposite of 238), which means it sinks the LED. Because I had been thinking about making a light driver board with transistors and couldn't find my PNP transistors, I nearly abandoned the project. Then I remembered that I have the CD4051. It proved much nicer for this kind of tinkering I must say. Durable too, as I had put a sticker on it to nicely label the outputs and avoid mistakes. Alas, I put the sticker on upside down and absolutely tortured the IC on the breadboard for 15 minutes. It got hot but somehow still (seemingly) works. Unfortunately the pinout of the CD4051 is a bit jumbled.

Here the circuit is powered by a Supercap, previously charged by a solar panel in a dumb way: regulating down to 2.5, then boosting output up to 5V. Seller only sent me one 2.7V 100F cap when I had ordered two to put in series.

Now, to drive the LEDs I might need a special board to produce the absolutely essential soft afterglow effect of light-bulbs. I've been meaning to design such a board for a pinball machine project too. I found that ~100uF worked well with my white LEDs & 220 Ohm (the actual glass is red but perhaps I'll use red LEDs). A diode or transistor could make sure the cap discharges through the LED but there's something going on with the GND and partially blocked caps that I don't quite understand still.

I also tried to get a circular, 8-stage astable multivibrator to work as an experiment but because they're analog they're quirky, and they use two resistors and one cap per stage.

A 10 second delay circuit can be useful in alarm systems and such. A simple one can be made using a cap discharging through the base/switch of a transistor. But, transistors are analog amplifiers and not digital switches. I used a LM358 comparator here to produce a digital cutoff threshold (A-D converter), mostly to learn how they work. I think it's better to use a 555 for something like this.

Microchip SBC

Edit: Updates on this project here.

Some progress on this WIP fantasy single board computer/controller MCU+ASIC. Targeting ZX Spectrum specs or above (see my ZX page). Controlling pins "live" via easy-to-use BASIC on a TV has some advantages as a learning platform. Being able to quickly draw and manipulate graphs would help a ton too. The problem is that video generation eats up most clock cycles. My idea here is adding GPU working in parallel so there will be no disruption to sensitive timings. There's stuff like IchigoJam already, but it does all sound and video in software on an LPC-something.

I had to go 3.3V to support SPI Flash without level shifter and 5V is kind of high for modern ICs anyways I hear. I don't like the inclusion of USB bloat, but it's likely needed so people can get up and running with a cheap generic keyboard. It's handled by an external MCU of some sort (needs an ICSP header). Doh. I forgot to add an LM386 under the audio connector. Amplifying is not the job of the MCU/ASIC. There are heat, current draw and isolation issues I suspect. Video signal resistors might need to be through-hole so they can be changed (some displays have special needs).

I'd like to beef up the internal RAM but MCUs like the 328P use SRAM which is actually quite expensive, even in the kilobytes (going 64KB everywhere possible would add a few dollars, not even considering how it affects wafer yields). I guess it's possible to access cheaper RAM via SPI but I suspect it'll be slow and only useful for storing banks. It's likely more useful to put FLASH on SPI and use as a disk.

This board (without MCU/ASIC) looks doable for around 15 buckaroos using low quantity china ebay prices as reference. It's possible to source cheaper components in bulk from manufacturers, but using ebay gives me some idea of retail cost (order processing, picking, shipping). The Microchip/Atmel MCU/ASIC doesn't exist of course and would be around 12 bazillion golds to develop, give or take. Ideally, retail price for the finished MCU/ASIC should be $5-12 depending on economy of scale. The product would be targeting hobbyists/students so it doesn't really compete with 3 cent MCUs or Raspberry Pi Zeroes which are different things. I think, if the board was sold as a kit with only SMD presoldered, the whole thing should be under $40 including profits. At $50 I would already be hesitant if I were some other bloke. A stripped down pirate board with a QFP-32 could be like... $15.

I accidentally made a radio trying to amplify something.

I wrote some more low-level port code for this USB Leonardo keypad just to complicate matters. Using the keyboard library a keypad is just a few lines. However, what becomes complicated is that different OSes use different key codes.

Photoshop Keypad symbols inspired by Alien.

A look inside my Amiga sound sampler. They were paranoid about reverse engineering or something else. Enclosure is generic. This sampler served me well though. It's strange to think about now... how much money it cost then to get basic functionality we take for granted now.

Blew up the bulk filter cap of a Dreamcast like a careless idiot.

Thought I'd make an egg-clock / timer using a 7-segment IC + 555, but it turns out most of my 7-seg displays are common anode (doesn't work with chip) and I don't want to use inverters. Abandoned for now. The 4026 is a counter, but something like the 4511 which takes binary input could perhaps be used as a 10 colour palette ROM outputting to DAC circuit then to VGA. Maybe too slow though.

I'm old enough to remember disposable flash cubes for cameras. This relic that I found in the garage is older... maybe the '50s?

I played CASIO's Cosmo Fighter as a wee lad. I wish e-paper displays had better refresh rates and could be used for B/W LCD style games. Had to draw what I think it could look like. Analog stick, slider, 3D engine and colour overlay HUD. I suppose a B/W hires LCD screen could work but maybe they don't really exist... OLED might, but they're a bit more expensive.

Roccat Lua reconditioned. The surface finish had rotted so I took it off with steel wool. It leaves an uneven scratched finish but it can be hidden by a polish using a minuscule amount of hand creme.

Coffee machines can be a fire hazard if left on by mistake. I think there's a heating element inside which is powered more or less straight from the outlet, similar to a water boiler or soldering iron. So, maybe no regulation for the light integrated into the rocker switch. It's kaputt. My mechanical solution is what it is.

Quick enclosure idea for solar power supply. I don't have any metal sheets though so not so quick to actually make. Front could be printed and laminated, and used as a drill template.

Photos/Art by Arne Niklas Jansson