Build 19 car security and remote sensing

[Mike]

Build 19B is available for download.

Car security mode
* Two alarm inputs send alert and location when triggered
* Remote starter disable by text message
* Remote horn/lights to locate vehicle or scare off a thief
* Remote door unlock by text message
* Power loss alert
* All normal tracker features

Remote sensing improvements
Build 19 can send INPUT and ALERT messages in text format, with a list of conditions and the status of each. For example:
ALERT GENFAIL- LOWFUEL- GENRUN+ REMSTART+ OVRCRANK- DISABLE- OVRSPD- SMOKE-
This is a generator monitoring example. There are up to eight inputs and the text labels can be customized.

Description and hardware photos here:
http://www.opengpstracker.org/build19.html

[aj7]

this is build is awesome! I'm just curious: what transistors and relays are you using to control things in the vehicle? Additionally, are you controlling the "control circuit" of, say, the starter relay, and not the actual power wire running to the starter?

[Mike]

I am using Zetex ZTX653 and some automotive relays from the Mouser catalog (551-ep2-3n1st). The relay coils use 12 volts.
The unit is not actually installed in a car. However, yes you would interrupt the low-current control wire from the ignition switch.

Mike

[aj7]

Ok cool. Except... mouser is out of 551-ep2-3n1st until late April -- Can you suggest another similar relay that will work please?

[aj7]

Would the BRIDGE version work? They seem to have that one. What is the difference?

http://mouser.com/Search/Refine.aspx?Keyword=551-ep2

[Mike]

You can use any 12 volt relay that provides enough contacts for the circuits you want to operate, and is rated for enough current.
Use two single relays instead of a dual relay.

Mike

[aj7]

I ordered 3 of the relays I mentioned above to try. What is the current that the uC outputs? What about the transistor?

What is the difference between a single relay and a dual and why would I need 2 relays?!

Thanks for your help -- I'm learning here

[aj7]

After reading the datasheet for the EP2-3N1S, I can't figure out which pins are for control and which are load -- help?

[Mike]

Yes, the diagram is confusing. I no longer have one of these relays.
Here is how to make sure you have the right terminals.

Measure ohms and find a pair with some resistance, not zero or open.
That's a coil. You should have two of them.

Find the pairs that are shorted. You should have two pairs of them.
Those are the Normally Closed and Common terminals.

Apply 12 volts to a coil and it should click. Now measure the pairs that were shorted,
and you can find the Normally Open terminal corresponding to that coil.

I tested the relay this way before doing any soldering.

Mike

[aj7]

Ah, yes, now I see that the diagram is showing a coil -- I thought that was a resistor.

NOW what my problem is how will the tracker output 12v? Isn't the whole point of this to SWITCH 12v on the load side of the relay? The transistor can't output 12v, can it?

Or perhaps... is the microcontroller hooked up to the base of the transistor and the transistor's collector is hooked to 12v and emitter hooked to the coil of the relay?