Archive for 2014

Arc Dimmer – Schematic

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I finally found some spare time to upload the schematic for the Arc Dimmer:
Arc Dimmer schematic 1/2 Arc Dimmer schematic 2/2

Everything should be straightforward so I’m just going to give you a few notes on the optional components. If you want to build a stand-alone dimmer which is controlled via buttons and/or potentiometers, place components R36-R39, C30-C31 and D30-D31. If you want to build an I2C bus-controlled dimmer, place components U30 and R30-R35 (with the exception of R32/R33). U40 and U41 are there just to provide different footprints on the PCB.

PDF version of the schematic can be found on the Projects page.


Arc Dimmer – Introduction

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My friend asked me if I could make him a push-button controlled LED dimmer, so I did! And went a bit haywire with the options list, as usual. Instead of making a single-purpose dimmer I decided to make it a bit more universal and bulletproof. Here are the basic specs:

  • operating voltage: 12-24V DC
  • load current: up to 10A (or more with a different output switch)
  • protected against overvoltage, overcurrent and overtemperature
  • two configurable control inputs
  • optional I2C interface for bus control
  • status and power LEDs

The PCBs arrived a few days ago and I assembled one unit for testing. A few parts are missing because they are on order and should arrive soon. Here are a few pics until I prepare the documentation:
Arc Dimmer PCB
Arc Dimmer Prototype
Arc Dimmer Prototype


UNI-T UT60E Accuracy Check

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Second multimeter that faced the DMMCheck Plus is the UT60E from UNI-T. It’s a 4000 count TrueRMS meter with much lower specifications than the UT71C tested previously. Let’s see if cheaper is really worse…or not.

As before, DMMCheck Plus with its specification sheet if anyone is interested:
DMMCheck Plus DMMCheck Plus

Both the DMMCheck and UT60E were left alone for around 30 minutes to get to know each other and for their references to stabilize (room temperature was 21C/70F).

AC/DC voltage measurement: passed!
UT60E AC Voltage Measurement - 5V RMS UT60E DC Voltage Measurement - 5V

AC/DC current measurement: passed!
UT60E AC Current Measurement - 1mA RMS UT60E DC Current Measurement - 1mA

Frequency and duty cycle measurement: passed!
UT60E Frequency Measurement - 100Hz UT60E Duty Cycle Measurement - 50%

Resistance measurement: passed!
UT60E Resistance Measurement - 100R UT60E Resistance Measurement - 1k
UT60E Resistance Measurement - 10k UT60E Resistance Measurement - 100k

I have to say that I’m pleasantly surprised with the results. Both current and resistance measurements were spot on which is incredible considering the UT60E’s specifications. Definately a permanent multimeter on my bench!


UNI-T UT71C Accuracy Check

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I borrowed a DMMCheck Plus from my colleague today and decided to check the accuracy of my multimeters. First up is the UT71C multimeter from UNI-T. It’s a 40000 count TrueRMS meter with decent specifications. Let’s see if it passed with flying colours or failed miserably!

Here is the actual DMMCheck Plus with its specification sheet if anyone is interested:
DMMCheck Plus DMMCheck Plus

And now let’s take a look at the results. Both the DMMCheck and UT71C were left alone for around 30 minutes to get to know each other and for their references to stabilize (room temperature was 21C/70F). UT71C is around 4 years old, with factory calibration.

AC/DC voltage measurement: passed!
UT71C AC Voltage Measurement - 5V RMS UT71C DC Voltage Measurement - 5V

AC/DC current measurement: passed!
UT71C AC Current Measurement - 1mA RMS UT71C DC Current Measurement - 1mA

Frequency and duty cycle measurement: passed!
UT71C Frequency Measurement - 100Hz UT71C Duty Cycle Measurement - 50%

Resistance measurement: passed!
UT71C Resistance Measurement - 100R UT71C Resistance Measurement - 1k
UT71C Resistance Measurement - 10k UT71C Resistance Measurement - 100k

And there you have it, not bad at all considering the price! I do have to mention that the current measurement was fluctuating a bit with the backlight on (it’s probably a good idea to replace the battery).

UPDATE: I stand corrected on the previously “failed” AC current measurement. According to the manual (which I haven’t fully read), AC current accuracy is lower than what’s indicated on the UNI-T’s web site and only valid within 10-100% of the range. I tried to measure 1mA on a 40mA range and that is lower than the 10% of the range to meet the specified accuracy. Big thanks to Wytnucls at EEVBlog Forums for pointing this out!


Starlight – Controller PCBs Arrived!

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Delivery of new PCBs was delayed because of the holidays but now I finally have a complete set so I can get to work on actual firmware.

Starlight Controller PCB
Starlight Controller PCB

Most of the parts are populated; all hand soldered because I was lazy to take out my hot air station. First attempt at TQFP soldering and all went well. Of course, nothing is complete without a bodge. I first soldered the 3.3V PIC instead of the 5V one so the power pad got lifted during desoldering. D’oh!
Starlight Controller PCB
Starlight Controller PCB


Starlight – Driver PCBs Arrived!

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Santa made me very happy the other day when I saw an envelope in my mailbox. Since I ordered two different PCBs I wasn’t sure which one was in the envelope but it turned out it was the Driver PCB for my Starlight Controller project. Excuse the crappyness of my phone’s pictures but my digital camera is on holidays until further notice…

Starlight Driver PCB
Starlight Driver PCB
And a short rant time! While designing the PCB I used the terminal connectors’ datasheet as a guide for hole placement. Apprently, I was looking at the wrong datasheet because my connectors hang off the PCB by 1mm. Instead of 10mm hole-to-edge distance my connectors have 11mm distance. Normally this wouldn’t be a problem but since this PCB is supposed to go into a DIN-rail enclosure I could face some problems later…
Starlight Driver PCB


Starlight Controller – Introduction

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A few years ago I made a simple stair lights controller for my parent’s house. Powered by a single PIC16F877 running at 20MHz it had 20 pwm channels and an RS485 interface that I never fully implemented (it simply wasn’t needed). Outputs were driven by BSP170 mosfets that turned out to be highly sensitive to ESD during soldering but pretty reliable when soldered to a PCB. As I was still learning how to program microcontrollers at that time I was fascinated by the things you could accomplish with a microcontroller so instead of having a simple one-by-one animation I decided that a wave-like effect would be better. Everything was placed on a single PCB with through-hole components and I was extremely proud of my work. This simple circuit ran flawlessly for the past 4 years until it met its archenemy – the water! As you already know, water doesn’t mix well with electronics and although nothing blew up (except the fuse in the power supply) there was severe oxidation all over the PCB and…well…now it’s time to make a new version. Bigger and better than before!

And so the Starlight project was born. Basic idea is something like this: provide a decent amount of PWM outputs for LED strips and avoid previous design flaws. And overcomplicate things, bwahahahaha!! Here are my initial specifications:

  • 24 PWM channels (because 24 is multiple of 8)
  • up to 1A of output current per channel
  • up to 4 digital inputs (for proximity sensors)
  • up to 2 analog inputs (for…something…a light sensor?)
  • CAN interface for future expansion
  • USB interface for configuration
  • a few status LEDs (because everybody loves blinking lights!)
  • optional configuration PCB for stand-alone configuration

I have already received one PCB for the PWM drivers and the controller PCB is on the way. Unfortunately, due to the holidays I didn’t have enough time to actually order parts so now I have to wait until everything arrives (a week or so). It’s very sad to look at the finished PCBs and not have the parts to solder…


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