Back To Video Basics With An ESP32 VGA Display

In a world where standards come and go with alarming speed, there’s something comforting about VGA. It’s the least common denominator of video standards, and seeing that chunky DB15 connector on the back of a computer means that no matter what, you’ll be able to get something from it, if you can just find a VGA cable in your junk bin.

But that’s the PC world; what about microcontrollers? Can you coax VGA video from them? Yes, you can, with an ESP32, a handful of resistors, and a little bit of clever programming. At least that’s what [bitluni] has managed to do in his continuing quest to push the ESP32 to output all the signals. For this project, [bitluni] needed to generate three separate signals – red, green, and blue – but with only two DACs on board, he had to try something else. He built external DACs the old way using R/2R voltage divider networks and addressed them with the I2S bus in LCD mode. He needed to make some compromises to fit the three color signals and the horizontal and vertical sync pulses into the 24 available bits, and there were a few false starts, but the video below shows that he was able to produce a 320×240 signal, and eventually goosed that up to a non-native 460×480.

It’s a pretty impressive hack, and we learned a lot about both the ESP32 and the VGA standard by watching the video. He’s previously used the ESP32 to build an AM radio station and to output composite PAL video, and even turned his oscilloscope into a vector display with it. They’re all great learning projects too.

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Hackaday Trims Its Own Resistors

There are times when you might want an odd-value resistor. Rather than run out to the store to buy a 3,140 Ω resistor, you can get there with a good ohmmeter and a willingness to solder things in series and parallel. But when you want a precise resistor value, and you want many of them, Frankensteining many resistors together over and over is a poor solution.

Something like an 8-bit R-2R resistor-ladder DAC, for instance, requires seventeen resistors of two values in better than 0.4% precision. That’s just not something I have on hand, and the series/parallel approach will get tiresome fast.

Ages ago, I had read about trimming resistors by hand, but had assumed that it was the domain of the madman. On the other hand, this is Hackaday; I had some time and a file. Could I trim and match resistors to within half a percent? Read on to find out.

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Fun Audio Waveform Generator Is More Than The Sum Of Its Parts

[Joekutz] wanted to re-build an audio-rate function generator project that he found over on Instructables. By itself, the project is very simple: it’s an 8-bit resistor-ladder DAC, a nice enclosure, and the rest is firmware.

[Joekutz] decided this wasn’t enough. He needed an LCD display, a speaker, and one-hertz precision. The LCD display alone is an insane hack. He reverse-engineers a calculator simply to use the display. But instead of mapping each key on the calculator and typing each number in directly, he only taps the four 1, +, =, and clear keys. He can then enter arbitrary numbers by typing in the right number of ones and adding them up. 345 = 111 + 111 + 111 + 11 + 1. In his video, embedded below, he describes this as a “rather stupid” idea. We think it’s hilarious.

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Logic Noise: Digital To Analog With An R-2R DAC

Making sound with digital logic usually calls for a Digital to Analog converter. Building one can be very simple, and the sound quality out of an R-2R Ladder is actually pretty good.

In the last edition of Logic Noise, we built up a (relatively) simple VCO — voltage-controlled oscillator — that had roughly one-volt-per-octave response. I even demonstrated it working mostly in tune with another synth’s keyboard. But what if you don’t have a control-voltage keyboard sitting around or you want to combine all of the logic-based circuits that we’ve been building with other circuits under voltage control? That’s where the digital to analog (DAC) voltage converter comes in.

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Your First Digital To Analog Converter Build

Have you ever built a Digital to Analog Converter before? This is a circuit that can take the 0 or 5V coming off of several digital logic pins, combine them together, and spit out one analog voltage that represents that value. If you’ve never made one, here’s your chance. [Collin Cunningham] over at Make put together another lab video about DACs which we’ve embedded after the break.

The circuit above uses an R-2R resistor network – often called a resistor ladder – which you can learn much more about from the reference page that [Collin] links to. Although a DAC in an IC package is by far the most commonly found application, we do see these R-2R networks in audio hacks from time to time.

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Halloween Props: Voice-changing Daft Punk Costume

[Dr. West] shared his Halloween costume with us; a Daft Punk inspired voice-changing helmet. He stared with a motorcycle helmet, cutting out a hole in the back for a sub-woofer speaker. Inside there’s an old computer mic and the amp circuitry for a portable stereo system. An Arduino is used to pick up the wearer’s voice from the microphone and perform the digital signal processing. Once the alterations have been made the signal is sent to an R-2R resistor ladder to perform the digital to analog conversion, and onto the amp for broadcast. Hear the result in the video after the break.

The rest of the helmet is window dressing. He found some kind of auto-body repair product called flex-edging to use as metallic hair. Those fins are accented with strings of red and blue LEDs. The faceplate finishes the look using speakers from the stereo system and a tinted visor.

He wan’t going for a replica, but we think his creation would be right at home with the look of the original.

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PIC Programmable Power Supply

This programmable power supply is the perfect addition to your bench tools. [Debraj Deb], who previously built a whole house power monitor, designed this build around a PIC 18F4520 microcontroller. The desired voltage is set with an attached keypad, resulting in a digital output on the 8-bits of port D. The port connects to another protoboard with an R-2R digital-to-analog converter resulting in the target voltage. A set of transistors amplifies the current and a power transistor then takes care of the final output. After the break you’ll find two videos, the first walks us through the hardware and the second demonstrates the device in action, along with measurements of its performance. This certainly provides a lot more functionality than an ATX power-supply conversion.

Update: A big thanks to [Debraj] who sent us a code package as well as the schematic (PDF) used during testing. We’re having trouble getting the code package up for download right now. Check back later, hopefully we’ll have it up soon.

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