4-20mA Panel Meter Teardown

I haven’t done a teardown in a while so I thought I’d share the insides of panel meter I recently found at a Sunday morning junk market for $5.

Below is a panel meter that has been used in some sort of industrial process. It was manufactured in 1980 by Kuwano. I’m not quite sure who the manufacturer was – the company’s logo is not easy to read but it might say, “Aumano”. What caught my attention with it was that it includes high and low needles as well as indicators and relay outputs for the high and low limits.

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Printing Heat Shrink Cable Markers with a Dymo Labelmaker

Recently I saw you can buy heatshrink tubing cartridges for Dymo label makers. This would be really convenient to make professional looking markers to identify individual wires and cables in some of my larger projects. (Cable and wire markers for industrial applications such as these have been around for at least a decade now, but are pretty expensive. This solution from Dymo seems to be somewhat more mainstream, but it still is too expensive for the hacker)

However, my hopes were dashed when I realised that the cartridges aren’t compatible with my $35 Dymo LetraTag. Also, each cartridge is $50, so I wasn’t keen on buying one hoping that I could get it to work with my label marker.

So I got thinking about making my own and I managed to cobble together a somewhat effective method using some regular heat shrink and some 180 grit wet & dry sandpaper.

Somewhat successful printed heat shrink cable markers

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Energy Meter Hacking – Reading EOUT Pulses

Following on from a recent teardown of a low cost appliance energy meter, I’ve done a bit more hacking of the device. As you may recall, I identified that one of the pins on the meter’s chip (EOUT) output a train of pulses proportional to the energy consumed. Some tests with a multimeter seemed to confirm this because the average voltage of EOUT changed with the appliance wattage.

I was hesitant to connect my logic analyser to the meter to measure the EOUT pin because of potential differences in voltage levels. To resolve, this I quickly whipped up a small board with a 4N25 opto-isolator to provide some voltage isolation between the internals of the energy meter and my logic analyser.

Again, I will repeat the obligatory warnings prevail. Do not:

  • Attempt or copy any of this if you do not fully understand or appreciate the hazards of mains power
  • Open the meter whilst connected to mains power
  • Perform any measurements whilst the meter’s case is open
  • Connect another mains powered device to measure the chip. The energy meter’s power supply is not isolated from active, neutral or earth.

The circuitry that allows for isolation of voltage levels is based around a 4N25 opto-isolator. An opto-isolator  allows for a signal to be transferred using light, this provides an airgap which provides electrical isolation.

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Da Vinci Extruder Power Connector Fail

The small quick release connector for the extruder heater recently failed. This was discovered half way through a print when the extruder stopped heating.

New Da Vinci heater connection

Initial thoughts were that there was a software bug due to the extruder failing to extrude filament after 12 hours of continuous operation. However, some fiddling with connections revealed that the plug and socket connection was the culprit.

Replacing the stock connector with something more robust is straightforward but the process is a little fiddly.

MicroLogix 1400 PLC Teardown


Introducing the MicroLogix 1400 PLC (1766L32BXBA) from Allen Bradley.

A PLC – Programmable Logic Controller – is a device that is widely used in industry for controlling electro-mechanical processes. They are a different beast to your Arduino – you don’t get much change from $1500 for this model PLC – being that they are more robust in construction and flexible to program (PLC ladder logic or statement list programming is a different approach than using a language such as C).

This model is considered a ‘shoebox’ PLC due to its size being about the size of a ‘shoebox’. It is by no means the largest or most powerful PLC that you’ll find but it is definately not a slouch for small to medium automation tasks.

A quick rundown on this device’s specifications;

  • 24VDC power input
  • 24x inputs – 20x digital and 4x analogue
  • 14x outputs – 12x digital and 2x analgoue
  • A combination of relays and FETs for the digital outputs
  • 12bit analogue input and output resolution
  • Each digital output channel can individually drive 2.5A
  • Individual ethernet and RS-232 communications ports
  • Input and output expansion cards can be added
  • A programmable LCD
  • Is fully operational when subjected to -20 to 60C temperatures

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