Old Dot-Matrix Displays Give Up Their Serial Secrets

June 4, 2024 by Dan Maloney 11 Comments

If there’s one thing we like better around here than old, obscure displays, it’s old, obscure displays with no documentation that need a healthy dose of reverse engineering before they can be put to use. These Plessey dot-matrix displays are a perfect example of that.

We’re not sure where [Michael] scored these displays, but they look fantastic. Each 8-pin DIP has two 5×7-matrix, high-visibility LED displays. They bear date codes from the late 80s under the part number, GPD340, but sadly, precious little data about them could be dredged up from the Interwebz. With 70 pixels and only six pins after accounting for power and ground, [Michael] figured there would be a serial protocol involved, but which pins?

He decided to brute-force the process of locating them, using a Pico to sequentially drive every combination while monitoring the current used with a current sensor. This paid off after only a few minutes, revealing that each character of the display has its own clock and data pins. The protocol is simple: pull the clock and data pins high then send 35 bits, which the display sorts out and lights the corresponding pixels. The video below shows a 12-character scrolling display in action.

Plessey made a lot of displays for military hardware, and these chunky little modules certainly have a martial air about them. Given that and the date code, these might have come from a Cold War-era bit of military hardware, like this Howitzer data display which sports another Plessey-made display.

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A PCB with an OLED display, a screw terminal block and a Raspberry Pi Zero board

Hackaday Prize 2023: Pi Pico Measures Volts, Amps And Watts

July 16, 2023 by Robin Kearey 6 Comments

Measuring a voltage is pretty easy: just place your multimeter’s probes across the relevant pins and read the value. Probing currents is a bit trickier, since you need to open up the circuit and place your probes in series. Checking a circuit’s power consumption is the hardest, since you need to measure both voltage and current as well as multiply them at each moment in time. Fed up with having to hook up two multimeters and running a bunch of synchronized measurements, [Per-Simon Saal] built himself an automatic digital power meter.

The heart of this instrument is an INA219 chip, which can measure and digitize voltage and current simultaneously. It outputs the results through an I2C bus, which [Per-Simon] hooked up to a miniaturized version of the Raspberry Pi Pico called an RP2040-Zero. A screw terminal block is provided to connect the system to the device under test, while a 0.96″ OLED display shows the measured voltage, current and power.

The maximum voltage that can be measured is 26 V, while the current range is determined by the shunt resistor mounted on the board. The default shunt is 0.1 Ω, resulting in a 3.2 A maximum current range, but you can get pretty much any range you want by simply mounting a different resistor and changing the software configuration. In addition to displaying the instantaneous values, the power meter can also keep a log of its measurements – very useful for debugging circuits that use more energy than expected or for measuring things like the capacity of a battery.

There are lots of ways to measure electric power, but they all boil down to multiplying current and voltage in some way. The multiplication was done magnetically in the old days, but modern meters like [Per-Simon]’s of course use digital systems. Some can even plug directly into a USB port. If you want to measure mains power, transformers are an essential component for safety reasons.

Supercon 2022: Irak Mayer Builds Self-Sustainable Outdoor IoT Devices

March 13, 2023 by Dave Rowntree 4 Comments

[Irak Mayer] has been exploring IoT applications for use with remote monitoring of irrigation control systems. As you would expect, the biggest challenges for moving data from the middle of a field to the home or office are with connectivity and power. Obviously, the further away from urbanization you get, the sparser both these aspects become, and the greater the challenge.

[Irak] solves his connectivity problem by assuming there is some WiFi network within range, building a system around the Blues Wireless WiFi note card. Substituting their cellular card would be an option for applications out of WiFi range, but presumably without changing too much on the system and software side of things. Leveraging the Adafruit FeatherWing INA219, which is a bidirectional current sensor with an I²C interface, for both the power generation and system consumption measurements. For control, [Irak] is using an Adafruit ESP32 board, but says little more about the hardware. On the software side, [Irak] is using the Blues Wireless NoteHub for the initial connection, which then routes the collected data onto the Adafruit IoT platform for collation purposes. The final part of the hardware is a LiPo battery which is on standby to soak up any excess power available from the energy harvesting. This is monitored by an LC709203f battery fuel gauge.

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Battery Analyzer Puts Alkaline Cells To The Test

April 20, 2021 by Tom Nardi 61 Comments

We know, we know. Generally speaking, you should try and switch your household devices over to rechargeable cells rather than using disposable alkaline batteries. But while they might seem increasingly quaint in the lithium-ion era, features such as a long shelf life make it worth keeping a pack of disposables around. So which ones should you buy? That’s what [Moragor] wanted to find out with his personal battery analyzer.

Designed as a shield for the Arduino Mega 2560, the analyzer combines a small programmable electronic load with a INA219 current sensor, OLED display, and SD card reader. The user selects the cutoff voltage and discharge rate before the test begins, and once it’s running, data is collected every second and saved to the SD card for later analysis. Once the battery voltage reaches the predetermined value, the test is over and you’re ready to put a new cell through its paces.

After testing 27 different brands of batteries, [Moragor] tabulated all the data and produced some helpful charts to illustrate the results. With few exceptions, the performance level for most of the batteries was remarkably similar. If anything, the test seemed to show that higher tier batteries from companies like Duracell and Energizer actually performed slightly worse than the mid-range offerings. Perhaps the biggest surprise is that, when the per-cell cost was factored in, the local cheapo batteries provided a better value than anything else in the test.

While the selection of battery brands may be different from where you live, the data [Moragor] collected is still a fascinating even if you don’t recognize some of the names on the chart. Of particular note is the confirmation that lithium batteries handily outperformed any of the Alkaline cells tested when it came to high-drain applications. We’d still rather they came in rechargeable form, but at least it’s a step in the right direction.

Versatile Energy Meter Has Multiple Functions

July 22, 2020 by Al Williams 10 Comments

If you are dealing with solar or battery power, you might want to have one of these little energy meters built by [Open Green Energy] around. The Arduino-based instrument measures DC voltage, current, power, energy, capacity, and temperature. The range is only up to 26 volts and 3.2 amps, but you could extend that with some external circuitry.

Of course, measuring a voltage with the Arduino is old hat. But the addition of a INA219 current sensor provides voltage, current, and power measurements in a single module that talks I2C back to the host computer.

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