Soft chippy, warm chippy, little chunk of RAM. Happy chippy, sleepy chippy, purr purr purr..

Like Sheldon Cooper, also the ChiliCAN needs a good night's sleep. I've been tinkering power optimization features and I must say the results so far are pretty good!

Here's the list of tricks that I've found by reading the datasheets and various articles on the web related to Arduino power saving:

• MCP2551 CAN transceiver can be put to sleep via the Rs-pin. Just control it via one of the Atmega328 output pins via 10k resistor (+5V in sleep mode, 0V awake), and we can save around 4 milliamps.
• Atmega328p has various power saving modes, and I wanted to use the most aggressive one (SLEEP_MODE_PWR_DOWN), which reduces the power consumption to less than few hundred microamps! It can then wake up with an interrupt generated by either the CAN controller or the GSM module.
• MCP2515 CAN controller has a sleep mode as well, enabled with SPI command. Before that we must enable the CANINTE.WAKIE interrupt signaling and connect the interrupt pin to INT0/1 on Atmega328p. Then, when a new CAN frame is received, interrupt is generated and the CPU can also kicked out of his silicon bed. Warning: The first CAN frame is always discarded and does not end up into the receive buffer (I think the sleep mode of both the transceiver and controller cause this). However in my setup it doesn't concern me, since the signal from key fob light button is not in the first CAN frame in the burst of messages sent to the bus when button is pressed and the car wakes up from its slumber. Another pitfall can be found in the wake up routine of MCP2515: If we want to wake up the controller (for example when the interrupt is generated by GSM module and not the controller), then it must be done by generating the CANINTF.WAKIF interrupt by ourself, and NOT the operation mode switch by SPI interface. The latter DOES NOT WORK! This is kind of weird, since the SPI interface is specified to be active even when in sleep mode. Reading its registers seems to work, but chancing the CANCTRL has no effect. Anyway, putting the controller to sleep gives us savings of around 3-4 mA.
• Ditch the AEM and consequentially, be able to get rid of the grounding relay as well. Naturally, this has no effect on sleep mode power savings directly, but since the relay is a power hog (~ 50mA when switched on!), getting rid of it enables us to use smaller and more efficient voltage regulator (those usually have also lower maximum output current). 
• Switch from 7805 to LM2936Z-5. The 7805 has in my tests shown quiescent current (waste current generated by the regulator even without any load) of more than 4 mA, where as the LM2936 is much more efficient, having quiescent current measured only in tens or hundreds of microamps, depending on the load. Unfortunately its maximum output current is 50 mA which is way too low if we want to use the GSM module as well.  

So, putting all the chips to sleep and using other aforementioned power saving tricks, I managed to get the sleep mode consumption down to 400 MICROamps! :) Now I don't have to worry anymore about accidentally emptying the car battery!  

Now, the measurements above are done without the Seeedstudio GSM module, because it is completely another beast: 

• The SIM900 GSM chip itself doesn't consume that much in sleep, its specified to be around  1-1.5 mA, but then again it has a peak current consumption of 2 amps during network registration and other wireless activity, which makes it little bit difficult to find suitable but efficient power supply. 
• The GSM shield has its own power regulator MIC29302BU. It is a low voltage drop regulator that can use Arduinos +5V and will provide 4.1 volts (adjustable) for the rest of the GSM shield to use. It is also able to handle the peak currents required by SIM900. Unfortunately it has a quiescent current of around 8 mA when idle, which is not that good.
• The shield has a "input power on" LED as well as an actual "power on" LED that is lit when SIM900 is turned on. I'm not sure of their forward voltage drop, so it's hard to guess their current consumption. It's maybe around 2.7 mA + 9 mA when fed with input +5V, if assuming voltage drop of 2.3 V (green SMD led). Also there's a orange GSM activity led, but it's on only intermittently (one blink every 2-3 seconds).
• The total consumption of the shield when the SIM900 is not even powered  is 12.6 mA! 
• When powered and in sleep mode, the consumption increases to 23.6 mA, having bursts of 36.2 mA every 3 seconds. 
• The total consumption of the whole device (7805 as the regulator, since LM2936 doesn't output enough juice for the GPS shield) when all the chips are in sleep mode is 27.4 mA (bursts of up to 40 mA every 3 seconds). 

It's quite clear that the SeeedStudio GPRS shield v1.4 is not designed for low power consumption in mind, otherwise it would have included a more efficient power regulator and a way to either disable the LEDs or give a way to control them for example with PWM. Since the MIC29302 is intended for automotive applications and has maximum input voltage of +60V, it should  be safe to power the whole device with this regulator. However while Atmega328p and MCP2515 can operate with 4.1V, the MCP2551 CAN controller needs at least 4.5V, which is then too much for the SIM900. So, another regulator is anyway needed.  

What about LM2936 for the main board and then power the shield with car battery directly? I looked at the LED configuration in the GSM shield schematics and found out that the LEDs are powered straight from the VIN (i.e. before the regulator), and if we give the shield input voltage of +12V without changing also the resistors, LED consumption would rise to tens of milliamps (probably burning them, if not at idle, but at least when the car alternator is running..)  So in this case little bit of resoldering would be needed anyway. 

Debugging in -25C...

Howdy!

The name of this post kind of says it all. Sitting in the car with a laptop and tapping on the keyboard while exhaling visible moisture which might make me look like a living steam engine. Trying to fix relentlessly the few remaining bugs, hoping that the laptop battery would last long enough, even though part of me wishes that the laptop would generate more heat.  At least the parking heater works!

For the past few days I've been building the remote heater starter and finally ChiliCAN v0.1 was born! It resembles little bit those implementations that I wrote about in the first post, but don't let the version number confuse you. This one speaks CAN and has multiple additional functions in addition to it's raison d'être: flipping on the relay and making the car a warm haven amidst the hostile environment that the Northern Finland is now at this time of the year.

Let's see what the little controller box has eaten: 

Ok,  it's not going to win any beauty contests, but it does what it's supposed to do.

The schematic is quite similar to what Arduino and the CAN shield would be when combined together. On the left is a separate USB breakout board, since it is not needed unless there is a need for debugging, giving manual test commands via the COM port or re-flashing the firmware. So the list of components is quite familiar: Atmega328p, MCP2515 CAN controller, MCP2551 can transceiver. A relay for grounding the AEM control pin (gives better isolation than grounding it directly via a transistor). The 7805 constant +5V voltage regulator + few passive components. Under the ribbon cable is also a SPI header for easy access to debugging with oscilloscope or maybe BusPirate (actually I ordered it a while back, but haven't yet tested it).

There's a extra 5A car fuse, isolated and kept in place with a hot glue, but now it's kind of deprecated since I have a main fuse outside the case for extra safety. Also the connectors are insulated with hot glue, and that with the IP65 protected case should give ample protection against moisture.  I still have to spray the board with a coating of protective lacquer, but that's only after extensive testing.

Then there's the female headers, resembling little bit the headers in Arduino board. And what's with the antenna?

Yup! That's the Arduino GPRS shield based on the SIM900 chip. I didn't have guts to start dismantling it, so I installed the Arduino type headers and laid the shield on top of the main board. I didn't want to use the built-in SMA-connector on the right side of the shield since that would cause both placement problems as well as increase my worries of poor insulation. So I used a left over WiFi SMA->U.FL extension wire from the Asus Maximus V Formula motheboard that I recently installed. I didn't have any use for desktop WiFi, so why not put the nice cable to use. Actually quite many of the parts here are left-overs or parts that have been recycled from old devices. There was also a long WiFi antenna included with the mother board, but I decided to use the one shipped with the GPRS shield.  

Sadly after preliminary testing I had to conclude that the Arduino+GRPS shield+CAN shield combination isn't going to work so nicely for two reasons. Separately they work quite fine, but all the combined code requires more memory than the measly 2Kb that theAtmega328p has to offer. This resulted in numerous random crashes, weird behaviour or just lack of functioning. This problem could be solved with optimization tricks, such as better memory utilization by removing unnecessarily large parameters and variables, and moving some parts out of SRAM to flash memory etc. 

However the much bigger problem would emerge when looking at the power consumption. Even when the sleep mode was enabled (in which text messages and calls could still be received) , the total amount of juice sucked by the device was around 80-90 mA. Although the sleep functionality of Atmega and CAN controller are not yet utilized by my code, the portion of power consumption by the SIM900 is almost half of the total even though it is in sleep mode ! Maybe I'm doing something wrong here, since according to the specs the GPRS module should consume only around 1-2 mA when dozing. 

For now as a heater start signal I will be using the yellow light button on the wireless key fob. Luckily the parking spot for my Volvo is almost right below my apartment window, so it is in the wireless range of the key fob and I will be able to use it to start the heater from the warmth of my house :) 

Pressing the light button 4 times (turning the car interior and exterior lights on-off-on-off in a time period of 10 seconds will start the heater. Turning it off is done in the same manner. I can also check the heater status with the fob: When pressing the light button  (regardless whether the sequence ends up in starting to heater or not), the car headlights are blinked 1-4 times. One blink means heater is off, two blinks: heater is either starting or stopping, three blinks: heater is on, four blinks: there is an error condition.

Here's the device ready for testing! Leftmost green led is for status. Next (yellow) is CAN traffic indicator (actually it doesn't blink for every CAN frame, since then it would just stay lit when connected to the car because of the huge amount of CAN traffic going on all the time. Instead, it blinks only when sending messages or receiving ones that have some inherent importance to us.).The third LED is a heater status indicator and fourth one is an error LED. I might later print labels and other stuff on the case with silk screen technique.

Here is the wiring harness for extending the AEM connector, nicely sleeved for making it look less like a botch job for what it really is. I tried for quite many hours to find suitable male/female connectors compatible with the 4-pin one that AEM and its harness has, but without any result. So I ended up having 4 separate connectors, one for each AEM pin. 

Then there are two DB9 standard CAN connectors. Leftmost has 12V connected to its pin #9 and is meant for connecting the ChiliCAN, and the right one is an extra debugging/tracing/logging CAN cable carrying only CAN-L, CAN-H and ground wires. Then there's extra fuse housing and the screw terminal to put the wires together. That + numerous cable ties give pretty good strain relief. 

I have to remind you that this is still going to be temporary installation as I may not even keep the AEM beyond the first few days of testing, so this not-so-elaborate setup will have to do for now.  Ok, so maybe I'm going to keep these in place until when outside temperatures are easier to count in celcius degrees than Kelvins.

Here's the final setup. Installing these separate dangling wires to AEM connector with  "relative safety" requires either that the negative wire from the car battery is detached or at least that the AEM fuse is removed. Also good electrical insulation tape is necessary. Did I mention botch job?

Later I might bypass the AEM connector altogether and connect the ChiliCAN directly to the Rear Electronic Module (REM) where the AEM wiring is originated.

Inspired by the stuff the guys at the Swedish Volvo forum have been doing, I too decided to add menu feature to the ChiliCAN. The menu can be accessed by keeping the cruise zero button pressed for two seconds.  The +/- buttons are used in navigating and another zero button press makes a selection. The return button exits the menu.

Using cruise buttons doesn't interfere with the normal cruise functionality unless we have turned it on before entering the menu. And even then the cruise buttons work normally and are not hijacked in any way.  Another, more familiar way of using the DIM menu would have been with SWM control stalk, but then we would have been forced to hijack the control stalk and I'm not sure if that can be done via CAN bus.

Heater can be turned on and off via the menu. Here it's status is shown (off / on / starting / stopping / error). It's handy to see the battery voltage without having to go crawl under the hood (or in case of S80, the trunk) with a multi meter. The various bits of information are queried by the ChiliCAN from CEM via diagnostic messages.

 It can be quite informative to see the coolant temperature here, since it gives rough estimation of how cold the engine is and whether you should start the heater. This makes it much easier to do rough guesses of how long should you keep the heater on to get the cabin and the engine comfortable. And of course, this isn't limited to the diesel/petrol parking heater, but could be used in conjunction with any additional heaters. When my Ardic broke down a while back, I got an electrical block heater (coolant heater) installed, but I wasn't (and still I'm not) quite sure how effective it is in hard metrics. With ChiliCAN I can now easily be able to see how well (or badly)  it really works.

One feature to tinker in the future would be the enabling of the water pump in Ardic in conjuction with the electrical coolant heater. That would give more even spread of the heat, since the block heater doesn't have its own water pump and is just heating one part of the coolant circulation, hoping that the difference in thecoolant temperature itself moves the liquid around a bit.

 Here we can see the GSM module status. Code isn't included in the firmware yet, since the memory optimization hasn't been done yet.


There is still quite a lot of things to do, but priority is now in lowering the energy consumption. After that, I might start thinking about having features little bit like what Volvo has to offer in their newest models: Volvo On Call mobile app :)