A Revolutionary Input Device, 30 Years Too Late

Way before you kids had touch screens and mice, we had to walk uphill both ways to tell a computer where we were pointing at on the screen. I speak, of course, of light pens. When these photodiodes in a pen were pointed at a CRT, the display driver would tell the computer where the pen was pointing. It’s a pretty incredible video hack today, and these things were around in the 1970s. You could, of course, use a light pen with most of the old 8-bit home computers, including the Commodore 64.

[Jan] has a soft spot for the light pen on the C64. So much so he made a new input device using this tech. It’s great, and if this existed in 1985, all the cool kids would have known about it.

The build is called the LightHammer. It’s a light pen, inside the head of a plastic hammer, with a few springs, nuts, and washers to tell the computer to read the light pen input. The light pen itself is just a photodiode with a few transistors; it was a simple circuit in the 80s, and it’s a simple circuit today.

A new input device isn’t worth anything without an app to show off the tech, and [Jan] is about three steps ahead of us here. He wrote a game for this LightHammer – a digital version of Whac-A-Mole and Simon. They’re exactly what you think they are: the classic ‘repeat the computer’ and ‘murder rodents’ games.

If that’s not enough, [Jan] also built an arcade cabinet for his C64 setup, with the monitor, joysticks, a 1541, and a TV mounted in a cabinet that would look great in a bar. You can check out a video of that and the games using the LightHammer below.

28 thoughts on “A Revolutionary Input Device, 30 Years Too Late

    1. I had forgotton that I built a light pen for the trs-80 back in the late 70’s. slow, sucky, but fun for a teen when the whole home-computer thing was still sci-fi to most people. iirc, a horizontal line was drawn from top to bottom and then once the line was found, it had to find the point. all in ‘user mode’ graphics, not any kind of hardware help at all. it was slow and it looked ugly, but it was NEW and there was no such thing as a mouse back then. hell, we didn’t even have lowercase unless you added an extra piggybacked ram chip (2102?) to bit-6 to get lowercase chars ;)

      it is fun to be reminded how far we have come and how short a time ago it really was.


  1. When used all day, lightpens caused RSI in the shoulder, neck and elbows. Mice are far more benign in this respect.

    I expect there to be similar problems with the vertical screesn on “touch enabled” computers. Lawsuits will follow, in a few years time.

    1. And to be even easier on yourself, try out a thumb ball (Logitech Trackman). Mice can lead to RSI injuries as well, albeit not as bad as light pens.

      Any artificial interface will lead to problems eventually, if overused. The real key to alleviating most problems is regular breaks and stretching the affected area once in a while.

      1. True, trackballs “compromise” your thumb’s “integrity”. So will trackpads: I’ve seen someone left unable to wash up, write, drive even after an operation.

        AI is a red herring in this context. In any case, I prefer artificial intelligence to natural stupidity.

  2. I like the approach to enhancing the arcade cabinet WAF and floor space optimization.

    Unfortunately my cats are slobs and I’d end up stepping in wet kibble an hour after feeding.

  3. In the mid-80s I built a light pen for my Apple ][ out of Nibble Magazine. IIRC, it was a photodiode, Darlington transistor, and potentiometer, with the pen itself being the shell of an actual Bic round pen.

    1. In short: no. Lightpens and lightguns rely on the sequential nature of pixels on a CRT, i.e. Each pixel is lit up one after another. You match the detection time of the pen to what pixel was lit up, and you get a position. On an LCD, huge swathes of screen are lit up at once, so it doesn’t work. On the other hand, for LCD’s you can use WACOM panels, depending on size. Bonus points, insane resolution in over 3 axes and no pen tether! Downside, cost.

      1. There’s no reason a LCD couldn’t light up pixels in order like a CRT. You’d need control over the software of course but as long as the refresh rate is high enough that you don’t see the movement it should work fine.

      1. This one is slightly unique in that it combines a lightpen with a modern accelerometer. And you can play whack-a-mole on the CRT screen. Deluxe light pens, back then, did have a nose switch so you could press down to imitate interaction so the idea is not exactly new but it’s cool to throw in an accelerometer because it increase the possibilities.

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