When we see [Ken Shirriff] reverse engineering something, it tends to be on the microscopic level. His usual forte is looking at die photos of strange and obsolete chips and figuring out how they work. And while we love those efforts, it’s nice to see him in the macro world this time with a teardown and repair of a 1960s-era solderless breadboard system.
If you’d swear the “Elite 2 Circuit Design Test System” featured in [Ken]’s post looks familiar, it’s probably because you caught his partner-in-crime [CuriousMarc]’s video on the very same unit, an eBay score that arrived in non-working condition. The breadboard, which retailed for $1,300 in 1969 — an eye-watering $10,000 today — was clearly not aimed at the hobbyist market. Truth be told, we didn’t even know that solderless breadboards were a thing until the mid-70s, but live and learn. This unit has all the bells and whistles, including three variable power supplies, an array of switches, buttons, indicator lamps, and jacks for external connections, and a pulse generator as well as a legit function generator.
Legit, that would be, if it actually worked. [Ken]’s contribution to the repair was a thorough teardown of the device followed by reverse-engineering the design. Seeing how this thing was designed around the constraints of 1969 technology is a real treat; the metal can transistor and ICs and the neat and tidy PCB layout are worth the price of admission alone. And the fact that neon lamps and their drivers were cheaper and easier to use than LEDs says a lot about the state of the art at the time.
Microcontroller addict [Debraj] decided to make his own programmable sine wave generator, and was able to put it together for under $40 USD. Other than low-cost, his list of requirements was as follows:
Dual sine wave output, synchronized
Frequency, Amplitude, and Phase control
Low harmonics under 1 MHz
Scriptable via Python
The heart of the project is the Analog Devices AD9833, a complete Direct Digital Synthesis (DDS) waveform generator system on a chip. If you’ve ever rolled your own DDS using discrete ICs or in an FPGA, you can appreciate the benefit of squeezing the phase accumulator, sine lookup table, DAC, and control logic all into a single ten-pin package. [Debraj] uses AD9833 modules from the usual online vendors for a few dollars each. He synchronizes the generators by disconnecting the reference crystal on the second module and driving it from the first one. The remaining specifications are met by the inherent characteristics of the DDS system, and the scriptable interface is accomplished with an Arduino controlling the AD9833 chips and two programmable gain amplifiers (MCP6S31). We like the confidence that [Debraj] displays by sketching the initial circuit diagram with a ball-point pen — check out the sketch and the final pictorial schematic in the video below the break.
This is a good example of combining off-the-shelf modules to quickly build a project. This approach is great for one-off builds or as a proof-of-concept test bed that can later be spun onto a custom PCB. Another reason to use modules these days is that the modules are often in-stock but the chips are unobtainable. Though it appears [Debraj]’s only needs one of these generators, it would be an easy board to layout and build — if you can buy the parts.
When working with test equipment such as oscilloscopes and function generators, it can be useful to take a screen capture. Historically this was done with Polaroid cameras that were bolted in place, but these days it can be done over a simple USB connection. [Majenko] didn’t like the Windows-only software that shipped with their Tenma 72-14110 function generator, however, and set about reverse engineering the USB protocol to create their own.
The hack was pulled off by running the original software in a Windows VM, while running Wireshark in the host Linux OS to capture the USB traffic. Once enough data had been captured, [Majenko] set about figuring out how the function generator formatted the screen data when sending it to the PC. Based on the fact that the data changed in length depending on what was on the display, it was surmised that the data was not raw, but compressed somehow. A hunch suggested it was probably some form of Run-Length Encoding, and this proved to be correct. With a little more digging and experimentation, [Majenko] was able to put together some code that netted a clear image from the device.
It’s a useful guide for reverse engineering image data, one that could prove useful if you’re tackling a similar problem on other hardware. We’ve seen some great reverse engineering efforts over the years, on everything from old video hardware to the Sega Saturn. If you’ve been diving deep into the secrets of software or hardware yourself, be sure to drop us a line.
If you need an oscilloscope, function generator, or other piece of kit for your electronics workbench, there are plenty of modern options. Dropping $4,000 for a modern oscilloscope is nice if you have the money, but if you’d rather put it to better use there are great options that don’t cost a fortune. There are some addons that can turn a smartphone into an oscilloscope but one of the best values out there are older pieces of equipment from the 80s that still work great. You can even upgrade them with some more modern features too, like [NFM] did with this vintage function generator.
This function generator is an HP3325A and it is several decades old, so some work was needed just to restore it to original working condition. The cooling fan and capacitors all needed to be replaced, as well as a few other odds and ends. From there [NFM] set about adding one of the two optional upgrades available for this device, the high voltage output. This allows the function generator to output 40 volts peak-to-peak at 40 milliamps. While he did have an original version from HP, he actually had a self-made design produced that matches the function of the original.
Even if you don’t have this specific function generator, this guide goes into great details about the functioning of older equipment like this. Most of the parts are replaceable and upgrades aren’t completely out of the question like some modern equipment, and with the right care and maintenance these pieces of equipment could last for decades longer.
A lifetime of amassing random pieces of test equipment has left me with a gap in my armoury, namely that I don’t possess a low frequency function generator. This could easily be addressed, but for two things. I have a love for exploring the cheaper end of exported electronics and my need for a function generator is less than my desire to spend significant cash. I’ve tried to balance these competing forces in the past by picking up an astoundingly cheap instrument; that time I ended up with a lemon, but will lightning strike twice in the same spot? I spent £10 ($13) on a different cheap function generator and set off to find out. Continue reading “Review: Unnamed Chinese DDS Function Generator”→
While it might be nice to use a $4,000 oscilloscope in a lab at a university or well-funded corporate environment, a good portion of us won’t have access to that kind of equipment in our own home shops. There are a few ways of getting a working oscilloscope without breaking the bank, though. One option is to find old CRT-based unit for maybe $50 on craigslist which might still have 60% of its original 1970s-era equipment still operational. A more reliable, and similarly-priced, way of getting an oscilloscope is to just convert a device you already have.
The EspoTek Labrador is an open-source way of converting a Raspberry Pi, Android device, or even a regular run-of-the-mill computer into a working oscilloscope. It’s a small USB device with about a two square inch PCB footprint that includes some other features as well like a signal generator and logic analyzer. It’s based on an ATxmega which is your standard Arduino-style AVR microcontroller but geared for low power usage. It looks as though it is pretty simple to use as well, and the only requirements are that you can install the software needed for the device on whatever computing platform you decide to use.
While the Labrador is available for sale at their website, it is definitely a bonus when companies offer products like this but also release the hardware and software as open source. That’s certainly a good way to get our attention, at least. You can build your own if you’d like, but if you’d rather save the time you have pre-built options. And it doesn’t hurt that most of the reviews of this product seem to be very favorable (although we haven’t tried one out ourselves). If you’d prefer an option without a company backing it, though, we have you covered there too.
If you have a modern function generator on your bench it is quite likely to contain a direct-digital synthesis circuit that creates arbitrary waveforms using a microprocessor controlled DAC. If you have a cheap function generator it’s likely to contain a one-chip solution that generates approximations to sine and triangle waveforms through modifying a square wave with a set of filters.
These methods both produce adequate waveforms for most of your function generator needs, but they are both far from perfect for the purist. Both methods introduce some distortion, and to address this [michal777] has produced a generator that takes the process back to basics with all stages implemented using building block ICs and transistors. The circuit follows the same square-wave-modifying path as the cheaper integrated devices, but with significant attention paid to the design to ensure that it does as good a job as possible. It also makes for a fascinating dive into function generator design.
The generator hardware has been neatly fitted onto a PCB with a riser for a set of front panel controls. He shares a few pictures of previous designs. We particularly like one that appears to have been fitted into a redundant cooking pot.