Saturday, May 28, 2022

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Mailbag #14 - all about the projects

A month or so ago I became enarmoured with a couple of projects in particular - one was from Great Scott who featured a PCB/Solder reflow project from Chris at AfterEarthLTD.

A smart person might wait until these are available for sale, but I'm not that person so I ordered the PCB and the parts to make my own version (hooray for open source).

Another great project emerged from the brain of Big Clive who designed a PCB to safely trickle charge NiMH and NiCad batteries. Again I ordered the PCB and some parts (to be honest I didn't really need the "parts" - just some nice 120Ω resistors in the end).

This mailbag is where some of these items happily arrive, next - to the soldering iron!




Friday, May 20, 2022

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LM3915 LED display driver

At least a couple of years ago I took delivery of LM3914, LM3915 and LM3916 LED display driver ICs.

The most common application for these devices is to drive an array of LEDs in response to an input (e.g. sound), to make a digital version of the analog VU-meter shown below.

The LM3914 can process an analog signal in a linear fashion, the LM3915 operates the same but in a logarithmic manner, and finally the LM3916 is logarithmic and has been specifically optimised for audio applications.

I found quite a few different circuits online which described the usage of this chip, and had couple of false starts as a result.

In particular, the microphone works w-a-y better with a simple amplifier between the microphone and the chip, and for that I used an LM358 OpAmp circuit as shown below.

The final result works so well it has rather unusually sat on my bench for a few days for fun, normally I dismantle such circuits pretty quickly. In fact is part of an intro for a future mailbag. Nice one!





Tuesday, May 10, 2022

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Unlucky mailbag #13

This week I claw open some mail (literally) and try to figure out in a hilarious fashion what I was thinking at time of order!


 

Saturday, May 7, 2022

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A box for all seasons

A little while ago on Twitter I saw a post from @sad_electronics about an online "box designer" for 3D printers.


I love to FreeCad as much as the next person, but this site intrigued me - could I really "whip up" a box in a few minutes and then print it out so that I could hold it in my hands a few hours later? My Precious!