I’ve been working on my K.U.D Meter on and off for over a year now; partly because I wasn’t quite sure how I was going to do it, partly because it was a real struggle to find some utensils which looked “good enough” and partly because my toddler kept wanting to help!
Well over the last month, I’ve finally found the time to actually try it again and here it is…
It, of course, utilises the Micronta 3001. I took apart the telescopic tubing and detecting pad. On opening it up it was a mess. The batteries had corroded and caused a lot of issues inside, it was never going to detect metal that's for sure. This wasn’t a problem though as I wasn’t going to use any of the existing circuitry anyway. I cut away some cables but I left in the original PCB because I wanted to keep the existing knobs without having to somehow create mounts for them. Maybe I'll revisit this in the future though.
I wanted to keep the original battery compartment but all the old terminals were corroded and really nasty looking so I ordered some more. I was erroneously sent terminals a little too wide but rather than fussing with sending back and re-ordering I just used some snips to trim them down. To make it easier to work on I then soldered a JST connector to the battery + and - terminals so I could disconnect it without risking snagging it.
For this initial meter, I wanted to just have a very simple circuit with a flashing red LED and the screen lit up. I drafted up a circuit in Tinkercad which is available here: https://www.tinkercad.com/things/1fQQk8 ... meter-2023
and tested it on a breadboard. Because I only needed 3v for this circuit I purchased from Amazon a bunch of “dummy
” batteries so there are only actually 2 AAs in there despite having space for 6. The red LED is self-blinking in that it doesn't require any sort of timer chip or microcontroller. The screen was originally going to be illuminated in a clear white LED but in the end, I thought green looked cooler.
The red LED comes out of a hole in the body, through a hole in the masher and then up to the top where it sits in a surface mount LED holder. Unfortunately during the drilling attempt, something must have slipped and it wasn't centralised. As this was already my second masher (the first attempt was a complete disaster) I decided to live with it and just drill the hole even bigger and use a washer to cover it. It's not a perfect solution but I was dreading making an entirely new third attempt and making sure all the other holes were in the right place and bent in the right way. It’s acceptable and if I find a smaller washer (that's still got an 8mm central hole) I'll swap it out so it's less obnoxious.
It took me absolutely ages to find a strainer spoon even remotely close to what I wanted. The one I eventually used was the best-looking spoon part, which for me was the most important. It has a curved handle which was not ideal but I managed to Dremel in a suitable curve for it to go in. There’s actually a piece of wood inside which it’s then screwed into via a hole in the handle to keep everything tight and secure. A chrome coloured end cap hides all the sins.
All in all, I’m very happy. It’s not perfect but it’s not like there are schematics of the thing we can use for full accuracy. We’re all just basing it off small slightly crappy angles in a couple of short shots. Plus I’ve got plenty of room inside for potential upgrades in the future maybe an Arduino and a speaker to make the needle go all fritzy and beep etc.Shopping list:
Micronta 3001 (broken) - Bought for £10.30 on eBay
Potato masher - 50p from the local market... but I bought 2 so £1
Self-blinking Red LED - Bag of 10 for £2.45
Green LED - Already had, probably about 10p each
Battery terminals - £2.50
Fake batteries - £4 although I could have simply soldered wires to join the terminals instead for free
Cabling - Various coloured cabling for the wiring which I already had. Let's call it 50p of wiring
JST connector - Bag of 10 for about £5
LED surface mount holder - £1.70
Washer - Few pence
Labelling - Few pence
Total spend around £30
If anyone has any ideas on how to use an Arduino to control the needle then let me know, please. In the future, I'd like to add upgrades but for now, just wanted to get the bare bones working.