Direct sunlight sensor

So why are you using digital media to communicate? I wouldn't use a microprocessor either. I'd use an FPGA, lol

My dad had a new car that left him sitting more than once and they couldn't find the trouble because it had cleared by the time they towed it back to the shop. After the third or fourth time they cam out to troubleshoot it in the intersection where it quit and found the trouble, the ECU, of course. I think they sent it back to GM where they found an output transistor was intermittently faulty. They had no way to detect that sort of failure and self diagnose it. Seems like one more pin on the connector and a wire back to an input would solve that problem for system critical outputs.

The sensor only needs to have a very slow response anyway, so why would it respond to people walking in front of it? When clouds are in the way both sensors will be shaded, so it shouldn't cause any problems. I'm not sure what you mean be the sun intersecting the extended plane of the wall. Do you mean self shading because the sun is blocked by the building?

maybe use something slower than LDRs, eg: thermistors.

The sensor needs to be quick so that the awning extension will stop as soon as the window is fully in shadow (plus a bit to prevent excessively frequent movement).

As for the extended plane thing, just after the sun has moved to a position where a wall is first illuminated, the shadows move very quickly. I think the awning needs to be extended some distance regardless of the sensor, again to avoid excessively frequent movement.

Sylvia.

I was wondering if you would have any control of the speed that the awning moves, so I was looking at the sorts of things available. I notice that you are re-inventing the wheel, because sun sensors (and wind sensors too) for controlling awning motors are commercially available.

It would not surprise me if such sensors were expensive, or perhaps you just relish the challenge of making your own. However, perhaps you could get some ideas from a sensor made for the job?

Such examples as I've found just extend the awning to its end stop when the sun is detected, and completely retract it when it's not. I want something smarter than that.

Sylvia.

Looking at the schematic for mine, the solar sensor goes straight into the air conditioning ECU. That ECU also has two thermistors of its own, one for the cabin temperature, and one for (I think) whatever the heater or evaporator core is currently putting out. The schematic also shows the engine ECU and its outdoor ambient thermistor, so I think it's telling me that the air conditioner listens to that over the bus, too.

How I think it works is that it mostly uses the thermistors and the desired temperature set by the user, like a thermostat, but that the solar sensor changes the slope of the curve it uses to drive towards the set point. It might also change the overshoot.

In other words, if you're 5 degrees F above the set point at night, it will run the blower on "low", and stop when it is 1 degree F below the set point. If you're 5 degrees F above the set point in the daytime, it will run the blower on "high", and maybe wait until it is 2 or 3 F below the set point to stop. The car company wants those MPG, but they also don't want sweaty drivers.

Starting in about 2005, things got pretty chatty in a lot of cars... if there's a sensor plugged into one ECU *anywhere*, most of the other ECUs can get its value over the bus. By 2010, for sure. (This is partly why Microsoft or Apple or Internet-connected anything, anywhere in the car, scares me a lot.)

Matt Roberds

You make it sound like the extension will be deployed from fully retracted to some significant extension. If that is done, then yes, fast reaction is needed, but once it finds it's position, it can operate with a much slower response time.

I'm still not picturing this, but that's ok.

It's not a one off. As the sun moves across the sky, the sensor will again be exposed and the awning further extended.

Sylvia.

I'm not clear what you are saying. Of course it will have to adjust multiple times during the day. But the movement does not need to be anything remotely fast, so the sensor does not need to be quick responding. Even if the awning has a little overshoot, that just means it will be a little while longer before it adjusts again. Any control system will have overshoot and a lag in response. The only issue is how much is acceptable and how much is too much.

I can't imagine the shadow of a passing bird or a person walking by would have to upset a device like this that is tracking the movement of the sun.

Why does it have to track the sun? Put the sensor at the bottom of the window. If it's in the sun, extend the awning until it isn't.

Commercially available awning motors are not variable speed. Short of modifying one or building one from scratch, I appear to have no way of achieving slow awning movement. I have to work with what I can get.

Sylvia.

They are fast? Then I guess you need a fast response when in motion, slow the rest of the time.

}snip{

How about intermittent adjustment? Let's say every hour (or 30 minutes or whatever you prefer) you switch on the tracker. It awns, maybe incredibly fast, and then it stops. After your preferred time window it tracks again.

joe

The usual thing they use to measure solar energy is a Pyranometer.

For whatever time of the year and the typical irradiance when no clouds are present at your latitude, this will tell you what you've got shining down on it.

boB

It struck me this morning that all you need to do is sense the elevation angle of the sun... half of a typical sun-follower sensor, then use your PIC to adjust the awning. ...Jim Thompson

I can't accurately position the awning, since I haven't found an awning motor that gives position feedback (or any feedback, come to that). There are some for roller blinds, but they're for indoor use only.

I'd have to implement something to sense the awning position, and that seems likely to work out even more complicated than sensing when the awning puts the bottom of the widow into shadow.

Sylvia.

Can you describe the awning and its mechanism? ...Jim Thompson

Maybe something like this...

...Jim Thompson