Budget Brilliance: DHO800 Function Generator

July 8, 2025 by Matt Varian No comments

The Rigol oscilloscopes have a long history of modifications and hacks, and this latest from [Matthias] is an impressive addition; he’s been working on adding a function generator to the DHO800 line of scopes.

The DHO800 series offers many great features: it’s highly portable with a large 7-inch touchscreen, powered by USB-C, and includes plenty of other goodies. However, there’s room for enhancements. [Matthias] realized that while software mods exist to increase bandwidth or unlock logic analyzer functions, the hardware needed to implement the function generator—available in the more expensive DHO900 series—was missing.

To address this, he designed a daughterboard to serve as the function generator hardware, enabling features that software tweaks can unlock. His goal was to create an affordable, easy-to-produce, and easy-to-assemble interface board that fits in the space reserved for the official daughterboard in higher-end scopes.

Once the board is installed and the software is updated, the new functionality becomes available. [Matthias] clearly explains some limitations of his implementation. However, these shortcomings are outweighed by the tremendous value this mod provides. A 4-channel, 200 MHz oscilloscope with function generator capabilities for under $500 is a significant achievement. We love seeing these Rigol mods enhance tool functionality. Thanks, [Matthias], for sharing this project—great job bringing even more features to this popular scope.

80s Function Generator Is Both Beauty And Beast

April 23, 2024 by Tom Nardi 13 Comments

You know how the saying goes — they don’t make them like this anymore. It’s arguably true of pretty much any electronic device given the way technology changes over time, though whether or not it’s objectively a bad thing is going to vary from case to case.

As a practical example, take a look at the insides of this 80’s vintage HP 3314A function generator shared on the EEV Blog Forum by [D Straney].

With multiple PCBs stacked on top of each other, it’s hard to imagine that more components could possibly be crammed into it. One board in particular appears to be an entire Motorola 6800 computer, something which today would likely be replaced with a single microcontroller.

Which is actually why [D Straney] shared this with us in the first place. After seeing our recent post about a modern waveform generator that’s basically an empty box thanks to its modern components, they thought this would be a nice example of the opposite extreme.

So, is it a good or a bad thing that test equipment isn’t made this way anymore? Well, it’s hard to argue with the improved capabilities, smaller footprint, and reduced cost of most modern gear. But damn is the inside of this HP 3314A gorgeous. As one of the commenters on the page put it, hardware from this era was really a work of art.

Arbitrary Wave Generator For The Raspberry Pi Pico

November 29, 2023 by Lewin Day 6 Comments

Once upon a time, if you wanted to generate some waveforms, you needed to buy an expensive off-the-shelf function generator or whip up a big pile of analog electronics. Not so today, when you can grab a fast microcontroller off the shelf and have it squirt out whatever fancy waves you might desire. That’s just what [rgco] did to build this nifty arbitrary wave generator.

The build improves on prior work by [rgco] with the Arduino Uno, with which they built a device that could output at 381 kilosamples per second, with each sample update taking 42 instruction cycles. Thanks to the Pi Pico’s faster clock speed and certain performance optimizations, they were able to up that to a mighty 125 megasamples per second, using the DMA and PIO subsystems to output a new sample every single clock cycle.

The result is a cheap function generator you can build with a Pi Pico and a handful of resistors, which will probably cost you the grand total of $12. It readily outperforms, at least in regards of speed, devices based on the AD9833 function generator chip, which only runs at 25 megasamples. Plus, that chip can only output sines, triangles, and squares!

Even a passable function generator can be a useful tool to have in the workshop, as we’ve seen before. Video after the break.

Continue reading “Arbitrary Wave Generator For The Raspberry Pi Pico” →

Weird 555 Function Generator Uses Feedback

April 12, 2023 by Lewin Day 20 Comments

There are plenty of designs out there for sawtooth and triangle function generators, many of them using the humble 555 IC. Few are readily voltage controlled, making them difficult to work with using a DAC, though. Enter this useful design posted to EDN!

The nifty design allows both waveshape and amplitude to be controlled via voltage. You could hook up a couple of potentiometers and call it done. Or, even better, you can control these parameters via PWM output from a microcontroller. Handy, no? It’s achieved by a fancy routing that sends feedback from the 555’s output pin to the CV input, instead of the usual design that uses the THR and TRG pins instead. The design also allows the production of both symmetrical and asymmetrical triangle waveforms, and as a bonus, the whole oscillator draws less than 4 mW of power.

If you’re looking for a nifty triangle/sawtooth generator that sits neatly in your otherwise-digital design, this could be for you. Or, you might like to explore the sheer mountain of other 555 hacks we’ve featured over the years. We even held a contest! If you’ve got new 555 hacks the world needs to see, don’t hesitate to drop them into the tipsline.

Impatience Is A Virtue When Testing This Old Maritime Teleprinter

July 16, 2022 by Dan Maloney 1 Comment

[Larry Wall], inventor of Perl, once famously said that programmers have three key virtues: sloth, hubris, and impatience. It’s safe to say that these personality quirks are also present in some measure in most hardware hackers, too, with impatience being perhaps the prime driver of great hacks. Life’s too short to wait for someone else to build it, whatever it may be.

Impatience certainly came into play for [Sebastian (AI5GW)] while hacking a NAVTEX receiver (in German). The NAVTEX system allows ships at sea to receive text broadcast alerts for things like changes in the weather or hazards to navigation. The trouble is, each NAVTEX station only transmits once every four hours, making tests of the teleprinter impractical. So [Sebastian]’s solution was to essentially create his own NAVTEX transmitter.

Job one was to understand the NAVTEX protocol, which is a 100-baud, FSK-modulated signal with characters encoded in CCIR 476. Since this encoding is also used in amateur radio teletype operations, [Sebastian] figured there would surely be an Arduino library for encoding and decoding it. Surprisingly, there wasn’t, but there is now, allowing an Arduino to produce the correct sequence of pulses for a CCIR 476-encoded message. Fed into a function generator, the mini-NAVTEX station’s signal was easily received and recorded by the painfully slow teleprinter. There’s that impatience again.

We thought this was a neat hack, and we especially appreciate that [Sebastian]’s efforts resulted in a library that could be useful to hams and other radio enthusiasts in the future. We’ve talked about some more modern amateur radio digital modes, like WSPR and FT8, but maybe it’s time to look at some other modes, too.

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Retro Breadboard Gives Up Its 1960s Secrets

March 13, 2022 by Dan Maloney 18 Comments

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.

As for the necessary repairs, [Marc]’s video leaves off before getting there. That’s fine, we’re sure he’ll put [Ken]’s analysis to good use, and we always enjoy [Marc]’s video series anyway. The Apollo flight comms series was a great one, too. Continue reading “Retro Breadboard Gives Up Its 1960s Secrets” →

Low-Cost, Two-Channel Scriptable Waveform Generator

March 5, 2022 by Chris Lott 14 Comments

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.

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