Arduino GSM module testing
Ever since I got my Leaf and discovered that it had an iphone app that I could get the battery SOC (state of charge) or start the charging or turn on the heat or air conditioning I thought I could do that with my 320. I have a lot of experience using SMS (txt messaging) to have machine to machine control from other projects that I have worked on. I did not think I would need to go to the trouble of making an iphone app because simple txt messaging can be used to control functions in the car. I knew there were a lot GSM modules out there and have been thinking about how I could control parts of the 320. A GSM module is just like a smartphone, it can send and receive calls, send and receive txt messages and even connect to websites. The GSM module has to be connected to some kind of processor so the txt can be processed and some action is taken. I chose to use the Arduino GSM shield module mostly because there is a GSM library with all the functions and example programs built right into the Arduino IDE. I thought it would make programming easy (an it did!). The Arduino GSM shield plugs right into an Arduino Uno board. To enable the GSM module to connect to the cellular network it has to have an activated SIM card. The Arduino GSM came with a SIM card, but it is for Movilforum network, which is based in Europe. That SIM card would only work with a phone on Movilforum network, not with an iphone or Android here and I want to use my iphone. I looked into what GSM networks are available here and found that T-Mobile is on a GSM network. I also found they have a great plan for what I want to do. It is a pay as you go plan and for $3 a month you get 30 txt messages or 30 calls. My experience with the Leaf app is that I do not use it every day so 30 txt messages seems like it will be enough once I get the car on the road. After 30 it is $0.10 per txt or call so another 30 would be another $3. During the development of the code for the first control function I blew through 50 txt messages. The first function I developed was the control of the heater blower motor speed via txt messaging. To accomplish this I first built a MOSFET module to control the speed of the blower motor. That MOSFET is controlled by a Microchip PIC processor to produce a PWM waveform. The duty cycle of PWM controls the speed. In the original setup the dashboard switch actually switched current to control the blower speed. What I did in this new setup was use the switch positions to be a different digital input on the PIC. Depending on which digital pin was set a different PWM signal is sent to the MOSFET to control the speed. Since the blower speed control now is digital I can have any other digital signal control it, independent of the switch position on the dashboard. For the GSM module, I had different digital pins on the Uno processor set depending on the txt message received and those lines were connected to the PIC. For example if I sent "Heat2" the GSM shield/Uno would set the same digital line on the PIC as the switch to set the blower speed to medium speed. The txt messages can be anything, they just have to be programmed in the control program on the Uno. There is one issue using a GSM module. For it to respond to txt message commands when in the car it always has to be powered. That means a 12V circuit has to be live in the car at all time. I was planning to have a small lead-acid battery because I also plan to have remote electric door locks. Anything with remote control needs to be powered all the time. The GSM and probably the door locks only draw a few milliamps when in sleep mode. But even that load can discharge a 12V battery if left for a month or two. That is what happened to my Leaf at the beginning of the winter when I was not driving it every day. There is one other issue using the GSM module to control functions in the car. The interface needs some type of password protection. In other words none of the txt commands will work without sending a password first. I don't think this is too big of a worry but easy enough to implement.
I also worked on testing LED headlamps and turn signal bulbs. I had purchased the LED headlamps a few months ago on EBay but had never tested them until now. They were rated at 24 watts so I wanted to see how that compared to the halogen seal beam headlights that were on the car. What I discovered is that the LED headlamps were well below 24W, more like 18W. The halogen headlights were used just a little more power, but the LED were considerably brighter, by a factor of more than 2. The turn signal bulbs were also quite a bit brighter than the standard 1157 bulb. But they used nearly 1/4 the power as the regular tungsten bulbs so all four turn signal bulbs can be replaced and will only draw what one tungsten bulb would draw.
A video of the GSM module and LED lamp testing can be found here
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