- The Problem
This project started as a way to warn autistic occupants of a home that they left the stove on for an extended period of time. Several solutions were explored.
..* A new stove with a "left on" alarm. Some stoves have this feature but a new stove was beyond the financial reach of this project. ..* Stove alarm phone app's but these require you to enter when you start the stove. Not a solution, really. ..* After-market stove alarms. These were too expensive also. ..* Clamp meter (about US$10) that measures appliance current draw without invasive wiring. Note that the clamp part of the clamp meter only works when it clamps just one of the wires of the two or three wires that make up a power cord. This usually means that you are required to split the cable so that you can clamp around just one wire. The idea of marrying a Bluetooth Low Energy (BLE) module (about US$10) and a piezo buzzer with the clamp meter was an afterthought.
- Ideas
The clamp meter was bought [Clamp Meter](http://www.aliexpress.com/item/Free-Drop-shipping-MT87-Digital-LCD-Display-Clamp-meter-Multimeter-Ohm-DMM-DC-AC-Current-Voltmeter/1874051779.html
The Bluetooth module was bought [Bluetooth](http://www.aliexpress.com/item/NRF51822-2-4G-Wireless-Module-Wireless-Communication-Module-Bluetooth-module-zigbee-module-DMX512/1928935008.html
I tried to figure out what chip the MT87 uses but was unsuccessful. It's probably close to a Intersil ICL7107 or clone. So some reverse engineering was in order. It was determined that the analog input to the chip was at D in the picture below and that the switched 3 volts from the MT87 battery was at the bottom of R45 at A in the picture below. Bring B low to turn on the piezo buzzer. C is the input for volts and resistance measurement. D is for current measurement. E is +3 volts and F is GND. The boards are wired as such:
| MT87 | nrf81522 |
|---|---|
| A | VDD |
| B | P0.18 |
| C | N/A |
| D | P0.01 |
| E | N/A |
| F | GND |
As far as programming, I used a ST Discovery board's SWD programming port and hooked it up like this.
NOTE: picture gotten from here
Here is the whole mess hooked up with the progammer
Here is the end product with the board hot-glued in and ready to screw together. I added in a jack for power with a 3.3 volt regulator soldered in at the jack. I had to clip off the header pins from the bottom of the bluetooth board to get it down in height so it would fit inside the meter.
- Programming
Note that the alarm will work without using Bluetooth. On a modified Nordic Android App (nRFTemp) the wattage shows up under temperature and the temperature shows up in the battery icon. See pictures below.
- Set up
Here are some notes on how to set it all up on Linux:
- Get Key from Nordic Semiconductor so that you can download: a. nrf51_sdk_v6_0_0_43681.zip b. s110_nrf51822_7.0.0.zip
NOTE: If you want to get an older version of s110 (the bluetooth part) try here: https://github.com/finnurtorfa/nrf51
mkdir -p ~/boards/nrf51822
unzip nrf51_sdk_v6_0_0_43681.zip -d ~/boards/nrf51822/s110
unzip s110_nrf51822_7.0.0.zip -d ~/boards/nrf51822/nrf51_sdk_v6_0_0_43681
cd ~/boards/nrf51822
git clone https://github.com/NordicSemiconductor/nrf51-ADC-examples
mv nrf51-ADC-examples/adc-example-with-softdevice nrf51_sdk_v6_0_0_43681/nrf51822/Board/pca10001/s110
# Get my Makefile and nrf51822.mk (above) and put in ~/boards/nrf51822, get main.c and
put in ~/boards/nrf51822/nrf51_sdk_v6_0_0_43681/nrf51822/Board/pca10001/s110/adc-example-with-softdevice/main.c
# you might have to be root for these, on my box I have a link from
/opt to my home dir:
lrwxrwxrwx 1 root root 14 Dec 14 2012 opt -> /home/rick/opt
mkdir -p /opt/CodeSourcery
wget https://launchpad.net/gcc-arm-embedded/4.7/4.7-2013-q3-update/+download/gcc-arm-none-eabi-4_7-2013q3-20130916-linux.tar.bz2 -P /opt/CodeSourcery
tar xzf /opt/CodeSourcery/gcc-arm-none-eabi-4_7-2013q3-20130916-linux.tar.bz2 -C /opt/CodeSourcery
I used openocd to program the part but had to get the very latest git:
sudo apt-get install git libtool automake
git clone git://git.code.sf.net/p/openocd/code
cd code
# read the INSTALL file or just do:
./bootstrap
./configure
make
sudo make install
Do one mod:
diff -b -c /home/rick/boards/nrf51822/nrf51_sdk_v6_0_0_43681/nrf51822/Source/templates/gcc/Makefile.posix.\~1\~ /home/rick/boards/nrf51822/nrf51_sdk_v6_0_0_43681/nrf51822/Source/templates/gcc/Makefile.posix
*** /home/rick/boards/nrf51822/nrf51_sdk_v6_0_0_43681/nrf51822/Source/templates/gcc/Makefile.posix.~1~ 2014-07-01 15:31:40.000000000 -0700
--- /home/rick/boards/nrf51822/nrf51_sdk_v6_0_0_43681/nrf51822/Source/templates/gcc/Makefile.posix 2014-08-11 13:31:35.000000000 -0700
***************
*** 1,4 ****
! GNU_INSTALL_ROOT := /usr/local/gcc-arm-none-eabi-4_8-2014q1
! GNU_VERSION := 4.8.3
GNU_PREFIX := arm-none-eabi
--- 1,4 ----
! GNU_INSTALL_ROOT := /opt/CodeSourcery/gcc-arm-none-eabi-4_7-2013q3
! GNU_VERSION := 4.7.4
GNU_PREFIX := arm-none-eabi
Then do:
cd ~/boards/nrf51822
make
It should build.