I want to build up my electronics capability to be able to design and build a medium complexity circuit and have a completed project and boxed project. The aim would be to do this in such a way that I am also able to share some of these learnings maybe through a set of blogs, tutorials, live streams or videos on YouTube, TikTok or Instagram.

LM3914

Some things that have been of interest recently in discussions with the kids, as I had them setup the first project in the Dick Smith Funway series was to light an LED based on sound. I brought out an LM3914 Bar Graph driver to highlight how a different voltage could light a different amount of LED’s using a potentiometer. Ofcourse I had a wrong connection, followed by shorting it using the potentiometer and making the mini trim pot glow yellow with the short circuit and let out some smoke. The pot now has a “weak spot” but mostly works. I missed the kids on having the opportunity to see the destruction. Maybe I do a few of these experiments with them, like how to reverse the voltage on a capcitor and bow it up, burn a fuse, burn a wire, make a spark gap etc.

I wanted to extend the idea of the LM3914 circuit to be sound activated, sort of a VU (Volume Unit) meter. Sort of like this one CircuitDigest: LED VU Meter using LM3914 and LM358 The idea here would be to maybe see how loud they can yell into a microphone to detect it on the VU meter. Also this would allow them to compare the “digital” nature of the LED VU meter and an analog one. Another extension would be to build out a VU meter with resistors and transistors, like the Funway Electronics II project.

Microphone Pre-amp

To do this, I would use an electret microphone and presumably I would need a pre-amp. There seems to be an interesting review of what an electret microhpone is in Hack-a-day: A Bit More Than A Microphone: The Electret Story - Jenny List - March 7, 2018 There is some discussion between using an Op-amp and discrete components in a series of blogs mentioning the 990 discrete op amp

  • https://www.hairballaudio.com/catalog/parts-store/discrete-op-amps/je-990-discrete-op-amp
  • http://www.johnhardyco.com/pdf/990.pdf
  • https://warmaudio.com/blog/is-a-discrete-mic-preamp-a-good-thing

Ofcourse there are some ready to go modules like

There is some discussion on the Arduino forums Microphone to Op Amp between the MAX9814 and LM358

Some YouTube videos:

  • build guide Building a DIY Mic preamp! - Thomas van Opstal

    build guide Building a DIY Mic preamp! - Thomas van Opstal

    more about how to build a complex kit

  • Simple inline microphone preamps part 1 - design & schematics Robert Jenkins Technolog Simple inline microphone preamps part 1 - design & schematics Robert Jenkins Technolog

Some more designs below:

  • https://www.instructables.com/Build-The-5-Microphone-Preamp/
  • Texas Instruments (PDF): Analog Engineer’s Circuit Non-inverting microphone pre-amplifier circuit
  • https://www.reddit.com/r/AskElectronics/comments/9237jk/microphone_preamplifier_circuit_and_understanding/
  • https://www.nutsvolts.com/magazine/article/how-to-design-a-microphone-amplifier
  • https://www.thatcorp.com/datashts/AES129_Designing_Mic_Preamps.pdf
  • https://www.eevblog.com/forum/projects/help-with-design-considerations-of-a-proper-microphone-preamp/

Function generator

Which brings me to, How to test such a pre-amp, or at least consistently set it off. Clearly I would need a Functionn Generator. I do have one under the house utilising an XR2206. These are cheap and easy to get on Aliexpress:

The following great video from Great Scott suggests DDS (Digital Direct Synthesis) is the way to go, but also reviews some Op-amp and XR2206 designs:

There are a bunch of other options:

Test equipment

At which point this leads me into another look at test equipment and the idea of building from scratch and augmenting with Arduino like this volt meter as inspiration:

  • https://www.instructables.com/Arduino-Precise-Accurate-Volt-Meter-0-90V-DC/

FNIRSI DPS-150

There is also a need for a smaller and USB-C powered power supply, in this case probably this off the shelf device might be the best. Some review notes from EEVBlog:

  • https://www.eevblog.com/forum/testgear/new-miniature-programmable-dc-power-supply-fnirsi-dps-150/100/

Errata

Back on the learning tack there are a bunch of articles from places like