Hardware

Hardware

• Hardware
  • PCB
  • CPUs and Radios
  • Radio stuff
  • Power
    • Running at low voltage
    • Energy Harvesting
  • Mechanicals
  • Sensors
    • Temperature
    • Humidity
    • Door/Window Open Sensor
    • Occupancy
  • Occupancy Sensing
  • Other
  • Displays / UI
  • Hardware Inventory

PCB

• PCB fabrication

CPUs and Radios

CPU/microcontroller/radio solutions being considered.

• PICAXE
• PIC
• Moteino
• Arduino
• JeeNode
• Nanode
• RadioBlock
• ZigBee

SilLabs F930 http://www.silabs.com/products/mcu/lowpower/Pages/C8051F92x-93x.aspx

See also some alternatives including ARM-based and another roundup.

Radio stuff

Power

Goal:

• Any battery-powered OpenTRV unit should if at all possible be able to run off 2xAA NiMH (~2.4V) or Alkaline (~3.0V) to minimise space, weight and cost, 3xAA if necessary for any components needing ~3.3V.

• Any mains-powered OpenTRV unit should be able to run from a standard USB-micro 5V high-efficiency phone charger (EN/IEC 62684) to conserve energy and keep cost down.

Caution on cheap USB chargers: http://budgetlightforum.com/node/18731 and that micro USB is fragile, thanks @stuartpoulton 2013/03/03.

Running at low voltage

• A pair of AA NiMH delivers ~2.4V. Alkaline delivers 3.0V.
• A PICAXE can run at 1.8V, many radios and sensors, only intermittently needing power, prefer 3.0V+ (eg 3.3V or even 5V).
• A spare output pin on the microcontroller running PWM with two caps, two diodes and a Zener (for safety), can as much as double Vcc, under software control.

Note that 08M2+/18M2+ PICAXE, RFM22/RFM23 radios, DS1306/DS1302/MCP79410 RTCs, and STTS751/TMP112/TMP102 temperature sensors (note different uncalibrated accuracies) should all operate from 2xAA NiMH (V2.2--V2.5) directly.

The JeeLabs AA Power Board "can generate a stable 3.3V from a single AA battery (Alkaline or NiMh)" and "uses an ultra low-drain LTC3525 boost regulator chip which draws only 7.. 30 µA in idle mode (depends on input voltage). The input can range from 1.0V to 5.5V ..."

Energy Harvesting

Mechanicals

Eg 3D CAD / CNC

Might use http://www.thingiverse.com/ as source of initial modules such as wormdrive (and to push completed items back to).

May be able to work with Wim V at http://kd85.com/ to 3D-print initial TRV cases in PLA (poly lactic acid) good to ~60°C or ABS at maybe EUR20 each in small quantities. May be able to pre pre prototype with rough shell and M30 screw first.

BG20130304: Upon seeing http://www.radiantcontrol.co.uk/products/air-temperature-controls/thermal-actuator-adaptors#more-702 Bruno said: "Aha! So M30 radiator valves are M30x1.5 or M30x1. The ISO standard only specifies M30x3.5 and M30x2 so it looks like I'll have to include extended sizes in my file and try with M30x1.5. This would explain why the screw didn't fit quite right."

Adapter rings used in TRVs have an ISO metric thread (http://en.wikipedia.org/wiki/ISO_261). Each thread is characterized by its major diameter D and its pitch P so given those two values, you can model the corresponding thread. The designation is of the form M D x P. So a thread designated as M30x2 is defined by D=30 and P=2. In addition to this, ISO 261 explictly specifies a limited number of standard combinations: for M30 threads they are M30x3.5 and M30x2. TRV adapter rings seem to use a finer pitch than that defined by ISO 261 as they use M30x1.5 or M30x1.

Possible 3D prototyping printer: http://www.maplin.co.uk/3d-printer-velleman-k8200-783902 (GBP700), uses PLA.

Some notes on transistor selection for an H-bridge motor driver: http://www.robotroom.com/BipolarHBridge4.html the favoured ones there being Zetex ZTX1049A/ZTX968.

DHD20130516: we had a useful IRC session about H-bridge direct motor drive, including http://www.earth.org.uk/OpenTRV/circuitFragments/MS20130516-hbridge-2wire.png outline schematic from Mike (only needs two digital lines to drive it) and http://www.earth.org.uk/OpenTRV/circuitFragments/MS20130516-hbridge-2wire.txt notes about current monitoring and supply management.

Stuart P points out the DRV8837 http://www.ti.com/lit/ds/symlink/drv8837.pdf which other than the tiny package looks like a good fit for us. Now (2014/07) have 3 on breakout boards.

Sensors

Temperature

Tested: DS18B20, OneWire: good accuracy but requires 3V--5V and is costly.

Tested: TMP102 (and TMP112), I2C/TWI: operation down to 1.4V and good accuracy.

See also for use of thermistor for good accuracy and low cost: https://mikestirling.co.uk/2013/04/low-cost-high-accuracy-temperature-sensing-with-a-thermistor/

For 2xAA (NiMH) operation (1.7V) and reasonable accuracy (+/-0.5C), the MAX31723 and DS7505 look good. (Also SE98A from NXP.)

Humidity

For RH (Relative Humidity), @oohshiiiny 2013/02/03 suggested looking at the DHT11.

As of the end of 2014 the SHT21 is being used in REV4 and REV7 boards.

Door/Window Open Sensor

• Wireless stick-on magnetic sensor
• LDR-based light-level sensor

Occupancy

PIR: Murata IRS-B340ST02-R1 / IRS-B210ST01-R1 ?

Occupancy Sensing

How to detect humans and avoid setting back the temperature and making them cold:

• PIR (passive infrared) low-power, low-voltage (2xAA) such as guts of http://www.minibattery.co.uk/05/led+light-UK/20129.html
• Ambient light levels (simple LDR sensor) or LED as output and sensor, eg http://www.merl.com/papers/docs/TR2003-35.pdf and http://blog.makezine.com/2009/08/05/ask-make-led-as-light-sensor/
• Optical proximity detection, eg Si1102, or MAX44000 which includes ambient level detection too.
• Detecting stray IR from any remote control usage in room (and allowing user to directly 'zap' the OpenTRV unit to announce presence and to operate the UI).
• Voice/sound/vibration (although vibration might travel too easily through the copper pipework) eg see AVR/ATmega FFT library http://elm-chan.org/works/akilcd/report_e.html and FHT (Fast Hartley Transform) code http://wiki.openmusiclabs.com/wiki/ArduinoFHT
• RH (relative humidity)
• Microwave (eg MWS-1 from RS), or HB100 Miniature Microwave Motion Sensor IM130619001 http://imall.iteadstudio.com/im130619001.html
• RF environment to determine occupancy (thanks to Philip J): http://ecs.victoria.ac.nz/twiki/pub/Main/TechnicalReportSeries/ECSTR12-04.pdf
• CO2 (currently very expensive)
• ultra-sound:
  • detect Doppler shift (as used in car alarms) (probably too energy-hungry)
  • or detect absorbance of ultra sound by human bodies
• Wimoto range: http://www.treehugger.com/gadgets/wimoto-adds-motion-and-water-sensors-wireless-sensor-system.html

Each has pros and cons, and more than one could be deployed at once.

Setback can be delayed a minimum time (or introduced gradually with increasing time) after a reliable indication of occupancy and/or a specific temperature target set-point in the schedule (ie always aim to hit specified temp/time points, but fall away from them gracefully in the absence of activity/occupancy). Manual switching from/to 'heat' mode also can count as a strong indication of occupancy and thus as a 'boost' signal implicitly.

My own (DHD) experience suggests that no sign of activity for 30 minutes fairly reliably indicates 'absence'.

A commercial system with occupancy sensing: http://acties.essent.nl/energie/warmwelkom/aanbod/index.html?ecmp=20120123SM004I

Other

@andybee (2014/12/14) suggests flood detection from the all-in-one valve units.
@brunogirin (2014/12/15) flood detection could also be done in partnership with http://oxfloodnet.co.uk/

Air quality sensors:
* CO2
* Particulates

Illuminance / light

Voltage

Current

Battery charge

Noise level

Movement (could be used to detect whether the device has been moved or tampered with)

Displays / UI

As well as LEDs and LCDs for visual display as part of a UI, here is an e-ink (non-volatile) display for Arduino/PICAXE: http://www.picaxeforum.co.uk/showthread.php?23583-E-ink-on-PICAXE-see-it-now-!

Audio output are also possible such as tone and speech http://www.techsupplies.co.uk/SPE030

Push-buttons, thumb-wheels and touch pads are easy UI inputs.

Hardware Inventory

i-Temp i30 TRV (DHD, in use)
PICAXE-08M2 Starter Pack (DHD, arrived 2013/01/17)
PICAXE Experimenter Kit (DHD, arrived 2013/01/17)
Various PICAXE spares including 08M2, 18M2, DS1307/DS1306+xtal, DS18B20 (DHD)
Arduino Uno (DHD)
Arduino Leonardo (lent by RW, 2013/03/16)
ATmega328P-PU (x2, DHD, arrived 2013/04/09)
USB-serial TTL cable, FT232RQ (DHD, arrived 2013/04/09)
MAX31723 thermometer acc is ±0.5C, res to 1/16C, supply 1.7V--3.7V, SPI (DHD 20130221)
DS1629+ thermometer and RTC (x2, DHD)
TMP112AIDRLT thermometer (x2, DHD)
DS1306 RTC (x2, DHD, arrived 2013/01/29)
DS1629+ RTC + temperature sensor (x2, DHD)
Conrad FHT8V TRV (x4, DHD, arrived 2013/02/18)
Conrad FHT8V TRV (DHD, arrived 2013/01/21)
Conrad FHT80BTF thermostat/scheduler (DHD, arrived 2013/01/21)
Maplin Tx 433MHz A58JN, aka RFM02 (DHD, arrived 2013/01/18)
Maplin Tsvr 868MHz A63JN aka RFM12 (DHD, arrived 2013/01/18) --> to go to BH
QAM-TX1 433MHz OOK/AM Radio Transmitter, dumb (DHD, arrived 2013/01/22)
QAM-RX2 433MHz OOK/AM Radio Receiver, dumb (DHD, arrived 2013/01/22)
HopeRF RFM22B-868-D 868MHz tsvr (DHD, arrived 2013/01/22)
HopeRF RFM22B-868-S1 868MHz tsvr (x2, DHD, arrived 2013/01/29)
HopeRF RFM23B-868-S1 868MHz tsvr (x5, DHD, arrived 2013/03/15)
Aurel TX-8L25IA 868MHz OOK/AM Radio Transmitter, dumb (DHD, arrived 2013/01)
AM-RRQ3-868 868MHz 'dumb' AM receiver (x2, DHD, arrived 2013/02/13)
Heatmiser PRT-ETS WiFi (underfloor electric, PC, 2013/02)
MAX!
- MAX! Heizkörperthermostat+ (TRV) (PC)
- MAX! WT+ Wandthermostat (thermostat) (PC)
- MAX! Cube LAN Gateway (PC)
X-10 kit including TM12 RF tsvr (DHD, from previous projects)

Misc support components such as LEDs, resistors, caps, sockets, etc.

Spare mechanical TRV valves, working and not, for testing (DHD)

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