Timer for car heater

[Jonas]

In the winter, when below and around zero degrees, I have a heater for my car connected to a timer. It heats the engine a bit to reduce wear and fuel consumption, but the main thing is the heater fan inside the car that gives me a varm and defrosted car when I'm going to work in the morning.
I want to build my own timer, a better timer.
It will read the outside temperature, and the colder it gets the earlier the heating will start, perhaps 20 min for each degree below zero.
It should have some kind of warning system if for some reason the heating dont start, maby I forgot to plug in the cable to the car or something.
Maby wifi so i can check the status from my computer or phone or just a 433mhz sender to a panel with a red and a green LED.
1. I need to get the RTC to work and make a timer.
2. I need to decide on the temp sensor, I have a DHT11, DS18B20 and various resistive sensors.
3. Thinking of using a solid state relay, and need to find out if a pyboard pin can handle the amp, or do I need a transistor to trigger the relay.
4. Build a weatherproof box.

I'm new to this so please join in if you want.

[bmarkus]

What is the operational temperature range of pyboard and other components you are planning to use? Not sure they are appropriate for car use.

[JasonHildebrand]

I am planning a similar project. One idea a friend of mine suggested is instead of using a relay to control the heater (which requires working cleanly with 120V), instead to use an inexpensive remote control power plug which can be controlled with a 433 Mhz transmitter.

This would allow you to keep your pyboard indoors, and simply run the temperature sensor outdoors.

I have been reading up on this approach and there are lots of posts of people hacking these plugs, including howtos and even fairly mature libraries available for other platforms like arduino and rasberry pi. For example, see: http://code.google.com/p/rc-switch/

In case it saves you time and research, I am using the following plugs:
http://www.amazon.com/Ivation-Programma ... 257&sr=8-1

I chose these over many other similar options because each outlet has a manual switch (many don't), the outlets remain "programmed" even after a power failure (many don't), and someone has helpfully confirmed hackability:
http://www.amazon.com/gp/community-cont ... B00N5152VS

I will be working on controlling this via 433 Mhz transmitter within the next few weeks.

RE: temperature sensors, I have been working on DS18S20 support. See https://github.com/micropython/micropython/pull/1095

[Jonas]

Great idea!
I already have a bunch of those remote control devices. I might use the remote wallswitch making the pyboard pull the button pins high or low.

I'm trying to read the DS18s20 sensor using this approach:

http://www.maximintegrated.com/en/app-n ... mvp/id/214

So far I have been able to reset it and then read one bit, now I just need to figure out how to read the rest of them.

[JasonHildebrand]

I have DS18S20 working for the simple case of a single sensor. I have updated my github tree, you need these two modules:
https://github.com/jdhildeb/micropython ... ds18s20.py
https://github.com/jdhildeb/micropython ... onewire.py

It doesn't yet support multiple devices attached to the same bus; I ported the search() method but it is not yet working. I don't anticipate having time to work on this for the next few weeks, so would be happy for help if you are interested.