• A Heathkit Oscilloclock!

    A Heathkit Oscilloclock!

    Anyone familiar with Heathkit®?

    From 1947 to 1992, the U.S. based Heath Company produced electronic kits for everything you can imagine: radios, TVs, computers, robots, ham gear, and electronic test equipment. Yes, you guessed it – they also produced kits for oscilloscopes!

    My Grandpa purchased one such scope, the Heathkit OR-1, around 1960. He wanted to kick off a new career in electronics repair, and the ‘build-your-own-equipment’ approach to training was in full bloom at the time. Also, since this was before the era of cheap overseas manufacturing, he could buy a Heathkit far cheaper than an assembled scope.

    Heathkit OR-1 manual - a work of art
    Heathkit OR-1 manual – a work of art

    Unfortunately, Grandpa’s electronics career never really took off. But decades later, he introduced me to his gorgeous oscilloscope, and boy – did that kick MY career off! Much later, the OR-1 came to live with me. (You can read a bit more about my affinity for this scope in my History page.)

    The problem is, I have too many oscilloscopes. But I don’t have enough Oscilloclocks. What more fitting way to keep Grandpa’s legacy alive, than to retrofit his Heathkit?

    Heathkit OR-1 Oscilloclock
    Heathkit Oscilloclock - Splash and Clock

    Special features

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  • Transformer Corner part 4

    Transformer Corner part 4

    Winding your own HV Transformer

    In Transformer Corner Part 3, I looked at how to choose materials for a custom HV transformer. One way was to pull stuff from the junk-box – I did this in my early Prototype. The much, much better way was to use an off-the-shelf core with documented specs.

    Let’s look at winding up the transformer. It’s amazingly easy to get a workable result!

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  • Transformer Corner part 3

    Transformer Corner part 3

    Designing your own HV Transformer

    In Transformer Corner Part 2, I looked at the power supply used in my early Prototype, and showed how to determine the key requirements for the HV transformer.

    Now, let’s see how I could choose the materials and design the transformer – without any pesky mathematical formulae!

    A hand-wound HV transfomer!
    The end goal – a hand-wound HV transfomer!

    Picking a core

    The first challenge was to find a suitable core from my junk box. First off, recall from Part 1 that this couldn’t be iron (too ‘slow’ for 151 kHz), and it couldn’t be air (too ‘weak’ for 25mA). I suppose I could have tried plastic, milk, or even beer – but I knew better. I knew about a substance called Ferrite.

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  • Transformer Corner part 2

    Transformer Corner part 2

    In Transformer Corner part 1, I introduced one of the key parts of the Oscilloclock – the HV transformer, and tried to illustrate some of the concepts and history behind it.

    Next, let’s explore the Prototype’s power supply configuration. This will tell us a lot more about the transformer I had to wind!

    Power supply design

    My greedy little Oscilloclock wanted lots of different voltages…

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  • Do chips have bugs?

    Do chips have bugs?

    There are probably many people who think that microcontrollers are bug-free. After all, they are glorified integrated circuits; a hard-wired jumble of infinitesimal transistor logic gates. There should be no unexpected behavior, as long as you operate the device within the rated voltage and temperature parameters….

    Wrong!

    What we tend to forget from our CPU architecture classes is that a CPU actually has a program inside. Known as microcode, its primary function is to interpret each instruction into the right electrical signals to drive the various parts of the CPU. For example, an addlw 0x7F instruction might involve directing the ALU’s input to the next word in program memory (0x7F), and then telling the ALU to add it to WREG, with output set back in WREG. The microcode for addwf MyVar would be different again; it needs to get a value in RAM, and set the result back there too.

    Well, where there is a program, there will definitely be bugs.

    My first experience with a microcontroller bug cost me several weekends of frustration, fretting, and frantic but fruitless rework. Here’s how it happened:

    Oscilloclock Gone Wild

    It was the early days of the Prototype, And things were looking great! My dream was coming to fruition! Except… every once in a while, the clock would go absolutely berserk. Seemingly at random, it would start displaying crazy, meaningless images, and controls would cease to function. Sometimes it would recover; other times, it would exhibit brain death – requiring a hard reset.

    April Fool's? No - it's a PIC bug!
    April Fool’s? No – it’s a PIC bug!

    No amount of testing or experimentation could tell me what the problem was. I rewrote huge blocks of code. I removed massive chunks to simplify the code. I drank more and more coffee. Sleepless nights and grumpy days ensued, wasting my precious youth!

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