Saturday, February 25, 2017

Piezo activated Drumlights - The Prototype

One of my colleagues is member of the Adelaide Samba drumming clum - SaSamba. I guess he was a bit jealous of the feathered samba dancers getting all the attention during a gig. So he brought up the idea of a sound/drumming activated light system for the band.

We aimed to get the set-up ready for the Adelaide Fringe parade. The parade takes place at night with plenty of opportunity to show off different sorts of lights.
Prototypes in assembly
For the first prototype I used an electret microphone with a pre-amplifier. With the right threshold tap and claps would activate the LED strips I had hooked up to it. It was only 5 RGB Led's on the test strip, but I was pushing my luck driving them directly from an Arduino Nano GPIO. An n-channel Mosfet is needed for safely sinking the current required for meter long strips.
The other trouble with this approach was the cross-talk between drums. Without fancy FIR filters identifying particular drums there was no reliable way of lighting only the drum being hit. In a band surrounded by screaming crowds an omni-directional electret microphone is definitely not the way to go.

After a conversation with Pix at the Adelaide Hackerspace I decided to switch to a contact-mic based approach, using a piezo as a knock sensor. Piezos can produce very large voltages in open circuit conditions, so I loaded this one with a 1MOhm resistor tacked directly onto the disk. Soldering on piezos is tricky, have to use flux, a hot iron and be quick. The disk acts as a heat sink and cools down pretty fast.

The piezo outputs only a few millivolts with this load (16-20 out of the 1024 max on the Arduino ADC range). This could be improved with pre-amp (opamp configured as a charge amplifier), however it is sufficient for thresholding and briefly flashing the LED's on drum hits.
Heatshrink as enclosures
My drummer colleague tested this with the whole band and it shows pretty good isolation as well. We went on to make 10 of these on protoboard and incorporated an overkill DPAK Mosfet (30V, 58A). These were covered in heatshrink and used with a lipo at the fringe parade in front of around 70,000 people. I wonder how many appreciated the fudging that went into making them.

Wednesday, December 7, 2016

Aliexpress DIN Rail Energy Meter teardown

The best way to learn is often by looking at solutions others have come up with. "Monkey see - monkey do" is pretty much part of the engineering process. While at University we wrote a top-scoring piece on how Apple scooped Creative in making a portable digital hard drive backed music player with great design and even greater marketing. When doing a tear down for inspiration and copying ideas always be wary of patents.

I am planning to move my ATM90E26 + Wireless Stack Energy monitor into a more industrial DIN rail format. To get an idea about how things are packaged inside a DIN rail energy monitor I ordered a no-patents cheap energy monitor with pulse output from AliExpress. The brand is Eastron, they also make quite affordable 3-phase versions which I am going to look at next.
DIN rail enclosure including wiring diagram
Once the meter arrived I did not even plug it in (in Australia an electrician will be required to properly install it due to the cutting of the live line to place a shunt and other modifications). I put a screw driver through the QC sticker, popped open the clipped on enclosure and proceeded to have a peek inside. What I found was a house of PCB's stacked around a transformer to make best use of the place inside the enclosure. The following labelled photos show the various parts.
Profile view with stacking

The stacking places the main processor board with AFE + MCU and LCD display on top, the transformer and associated carrier and high voltage safety stuff (Varistor and PPTC) at the base. The base PCB also carries the Live/Neutral connectors and a bulky current shunt. One vertical PCB is the power supply, voltage and current waveform sampler and the other is an isolated pulse and modbus output board (Modbus chip is unpopulated in my pulse only version).
Bottom view with safety components and current shunt
The voltage sampler uses a resistor ladder of 4x270K resistors in series with a relatively small voltage sampling resistor. The PCB is not heavy on expensive board to board connectors, which allows a modular system and swapping of boards, instead it relies of solder fingers on board edge to link the boxy shape together. The same board also carries the power supply module derived from a regulated full wave rectified output from the transformer. I am not sure if the transformer is isolating, it does not need to be since the isolation occurs at the end stage with a couple of optocouplers. The voltage sampler and the current shunt are obviously non-isolated.
LDO for dual voltage level output and 4 pads for 2 waveform signals
All the magic of actual energy monitoring then happens in the Vangotech V9811S with includes a 8052 MCU for driving the LCD and other functions such as Modbus support. I am planning to power it up with a 3.3V/5V supply and feed it waveforms from my low voltage AC test rig and observe the readings. I also have 3 phase version from Eastron on order and a few engineering samples from Vangotech for their 3 phase ASIC to build a low cost/ low voltage Dev kit like I did with the ATM90E26 Featherwing.
Anatomy of the head, MCU + AFE, EEPROM and an old school LCD

Wednesday, November 30, 2016

Adelaide Maker Faire 2016

Last Sunday (6th of November 2016) I spent almost the whole day on my feet talking to people at the Adelaide Maker Faire. It was a great event and I have been looking forward to it for almost a full year.

It took a bit of preparation in putting together a demo that would pass the electrical safety requirements and be tested and tagged. I chose to use a compact fluroscent lamp and a halogen lamp as my demo loads to illustrate the impact of power factor on energy measurements. The modern CFL's have notoriously low power-factor due to the uncompensated choke in them. I ended up making an earthed and a double insulated enclosure for my demo.
Earthed Test lamp box
Double insulated test lamp box

Earthed lamp fixture with Perspex lid

The main PCB on show was the Energy Monitor Featherwing with the ATM90E26 on-board. This does very quick and accurate measurements and I chose to send the data over serial to a laptop for graphing rather than use the rather crowded wifi and 3G environment at the faire. It also makes a more compelling demo since I can sample and display the power every second rather than every 15s with thingspeak (faster with workarounds still only down to 2s due to 8 channel limitation, must investigate running my personal Blynk or EmonCMS server).
ATM90E26 Low-voltage Energy Monitor (perspective view)

ATM90E26 Energy Monitor top view
My overall display was pretty minimalist since I focused on getting the hardware working rather than producing any marketing material. I ended up handing out notes written on the spot with my details on them. There was fair bit of interest and some people shared ideas with me on how they had solved the same problem themselves. I hardly got time to check out other displays myself. Next time I will make sure I have someone to relieve me. I did manage to have a peek at the Daleks and saw a toddler hop out of a solar car, sights you can only see at a Maker Faire. This was southern hemispheres biggest and the buzz was amazing.

Maker Faire setup with lamps on
At the end of the day the organisers of the Maker Faire handed me a maker of merit badge which I am quite proud of and next year I plan to show up with even more projects.

Monday, October 10, 2016

ATM90E26 + ESP8266 Energy Monitoring

Before I commit a design to a PCB, I usually make a messy jumpers everywhere version on a breadboard. This is not always possible for a full complex design, often sections get committed to PCB and then modules find a home on the overall breadboard prototype.

This has been the fate of my ATM90E26 Breakout. I plan to eventually make it into a single board /accurate wifi enabled Energy Monitor. For now it is living next to a NodeMCU on a breadboard. The ATM90E26 has the flexibility to be accessed both over SPI and UART. However the SPI mode it supports is only Mode 3, which is an unsupported mode of the ESP8266 Arduino stack. So I ported my ATM90E26 Arduino interface code over to UART mode with CRC check and everything worked okay after a few days of head scratching. You can find it on the UART branch in github.

I would like to build a self-powered energy monitor, so I pulled out a venerable 7805 and added it to a half-wave rectifier from the 12V AC-AC transformer used for voltage waveform sampling. When I was using a full-wave rectifier in the past the overall DC voltage was too much for thr 7805 to regulate without a heatsink, however with the 1/2 wave version, the diode takes care of dropping half of the voltage leaving the 7805 functional without a massive heatsink.

I calibrated the set-up with some magic multipliers found using the datasheet, maths and my 116W calibration lamp and it all works like a charm as shown in the video below.

There seems to be some noise leakage onto the UART when AC signals are applied, I will attempt to rectify this with an optoisolator. However a simple reboot of the ESP8266 platform seems to quickly fix any software serial communication issues. Meanwhile I am putting it all together into a featherwing form factor for PCB manufacture.

Sunday, September 11, 2016

Hexiwear based GPS-AHRS for Nikon hotshoe

I have been working on the GPS-AHRS hotshoe for a while. The initial complete prototype was built around the Xadow platform. It is one of those continuous iteration projects, I wish someone puts me out of misery and brings out a COTS solution that is affordable soon.

I put the idea for the GPS-AHRS on the Hexiwear platform and received a free Hexiwear dev kit to built it with, a great deal. The Hexiwear has lots of toolchains for building projects with, including the Kinetis Design Studio from NXP and ARM MBed. This makes development on this platform a breeze. It also comes with a lot of sensors : barometer, gyro, accelerometer and magnetometer are all included. It has built in BLE for communications and a 16bit OLED screen. The only missing links are GPS, Nikon camera interface and a sensor fusion algorithm to obtain Euler angles/quarternions from raw motion data.

I already have working MBed code for sensor fusion and I have successfully tested reading all the motion sensors over I2C, so this should be easy to put together in the next few days.
I also compiled the stock firmware in KDS and did some small changes to show the Magnetometer data as part of the UI. This was relatively simple simply involved attaching a listener to one of the messages already being broadcast in the RTOS and a hacked up page to display the results. The results of this code can be seen below.

Tuesday, August 30, 2016

Counting Pulses with Maxim DS1682

I am often asked about interfacing the Energy Monitoring system with traditional spinning disk meters or blinking LED/Pulse type meters. For this application there used to be a very nice 1-wire pulse counter IC from Dallas/Maxim - DS2423. However it is end-of-life and no longer available. The next best option is the DS1682/83 series of RC oscillator based elapsed time recorders. The elapsed time function is not critical for pulse counting, however it is a nice feature. The lack of crystal makes is slightly inaccurate, but pretty robust and great for outdoor and industrial applications. It also has an EEPROM to store counted pulses, so the counts are retained across power cycles and the main MCU can sleep between long interval reads.

To test out this chips I built a Grove breakout which I am planning to use with a tipping bucket rain gauge. I have tested it on the ESP8266 with some basic Arduino I2C code and theres seems to be already existing Python code I can extend to use with my Udoo Neo Weather station.

Pulse counting can be easily done using a GPIO and an interrupt, however it requires the MCU to be constantly on. The DS1682 has a 17bit event counter giving it 131,072 total event counting ability before a reset is required.

Monday, August 29, 2016

AWS Summit Sydney 2016

Any web application that targets a mass market and wants scalability ends up in the cloud, rather than in an individual data centre. Of all the cloud providers the biggest currently is Amazon. After running the metromap application with AWS for a year mostly on a self-taught basis I realized that it was time to rub shoulders with some experts and possibly bring in some help.
Amazon was hosting a sort of marketing conference in Sydney and unlike the academic conferences I am used to attending this one was free. So I signed up for it with some work backing.
On arrival I walked into a massive Kogan keynote speech, it had all the pomp and fanfare of a boxing match or WWF rumble. Felt very American.

There were lots of AWS customer stories including one by Origin Energy about customer analysis. They have over 100million customer interactions. Traditional meters are read only 4 times a year, while Smart Meters produce data at a 30min interval. With this data Origin can offer a fixed bill plan using predictive analytics. The creation of this service started in stealth mode hotel wifi and personal CC, interesting collision of corporate culture with internet realities.

Moving data to and from the cloud was big sticking point as well and the AWS Snowball (80TB) was announced. I have recently ordered one, still waiting for it to turn up. Will write another article on this Data Exchange unit once I have had a real life play with it. Working at an aerial photography company I am used to huge amounts of data coming in from aircraft on similar hard drive units, but none of them feature 10GB ethernet and in transit encryption like the Snowball does.

There was a big focus on IoT capabilities in AWS as well including an Earth, Air, Fire and Water demo with Alexa playing stage manager.

I had a small blast from my CSIRO past. Peter Blaine had a talk about IMOS data sharing. 50Million NetCDF's are up in the cloud. The big challenge being the heterogeneity of the data. Apparently they have moved to the warehouse next to my old office and things are progressing okay. Even though CSIRO is rapidly shedding science staff, the engineering half is still alive and well.
On the display floor I managed to knock over a remote presence bot and chat to a lot of people in various booths, including Sumo Logic and Puppet which were particularly relevant to my application of image serving and service monitoring.
After a couple of days of hard conferencing and networking I managed to get in some R&R and learn the weird game of shuffleboard and enjoy some cocktails at the Little Darlin'. It was an exciting couple of days in Sydney and since then I have been putting my knowledge to good use. I will write up another post from my mass of notes collected during the summit.