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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Ridiculously Simple Flex Sensor

New Scientist recently detailed the construction materials for the simplest flex sensor I’ve ever heard of – a graphite pencil and a piece of paper. It is obvious when you think about it, but as New Scientist details in in their article Pencil lines as sensors, 21st March 2015 (No 3013) edition,

“MacGyver would be proud. Drawing a rectangle on a piece of paper with an ordinary pencil can create a sensor.”

Draw me a flex sensor?

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Flatbed Scanner CCD Reverse Engineering

Probably about 12 years ago, I recovered the imaging sensor from an A4 flatbed scanner that had become obsolete. (I think its obsolescence was due to it having a parallel port interface and my family’s new computer didn’t have a parallel port) Apart from it not being able to communicate with a new computer, it still worked fine sadly. Fortunately, there were several useful components that I recovered from it including a stepper motor, v-belts and pulleys, CCFL light and the CCD.

Well, after all that time saying that one day I’ll get the CCD to work, the time has come.


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Energy Meter Hacking

Following on from the recent teardown of a cheap energy meter, I thought there might be some potential to hack this device. Well the EOUT “pulse output” pin shows some promise. The chip’s datasheet says that the EOUT pin outputs a pulse for each unit of energy the meter measures. Additionally, this function is enabled by default.

Since this is enabled, by default, I made some mods to the case and soldered 3x wires directly to the chip.

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TO220 Single and Dual Gauge Packages

A friend of mine recently asked me if I knew that there are two package types for humble TO220 devices. I didn’t understand what he meant. He then asked if I had heard of single gauge and dual gauge TO220 packages. Nope still no idea. Finally, he asked if I had seen TO220 voltage regulators such as a 78L05 device with a thin heatsink?

Yes, I had seen these before, in fact I have a couple. I hadn’t really paid a lot of attention to the first time I had seen one of these components with a thin heatsink. I thought that it was perhaps a counterfeit device. That is not the case (excuse the pun). A thinner heatsink is a type of TO220 package.

Below are two TO220 devices, a 7812 12V regulator manufactured by On Semiconductor and a TIP31 NPN transistor from ST Microelectronics. A quick glance and their shape is instantly recognisable.

TO220 devices
TO220 packages for a 7812 12V regulator and a TIP31 NPN transistor.

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MJE3055 Power Transistor Teardown

Whats inside a power transistor? Well some semiconductor to be a transistor of course. How large would you expect the transistor’s die to be?

My guess is, that for a device that can conduct up to 10 A, the die would occupy the bulk of the transistor’s package. What’s your guess?

MJE3055 NPN transistor
An MJE3055 NPN transistor ready to be dismembered.

Lets find out with a teardown of sorts with the following MJE3055 NPN power transistor that comes in a TO-220 package.

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Skillet Reflow 0603 SMD Capacitors = Tombstones

A recent project involved using an electric skillet to reflow solder some APA102C RGB LEDs to a PCB. The aim was to make a device similar to the Adafruit Neopixel Strips, but arranged in a 3×3 square and using the APA102C LEDs.

Honestly, each board that was made was a fail. Electrically, they all worked correctly. The failure was during the manufacturing stage – reflow soldering very small SMD components.

Just as an aside, Adafruit Neopixel devices use WS2812B LEDs which have some very strict timing requirements – this can be problematic for some devices that use software interrupts. Whereas, the APA102C LED is a chip that does not suffer from strict timing.

Each small PCB, contains 9x APA102C SMD LEDs and 8x 0.1uF 0603 ceramic capacitors for power supply decoupling. Each APA102C LED is the large white square with white circle. Between the rows of the APA102C LEDs are the SMD pads for the 0603 size capacitors.

PCB layout for APA102C LEDs
Top surface of the PCB layout.

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