# Wireless Sensor for detecting light

1. Aug 7, 2007

### robhoski

Here's a tough one:

How could one create a sensor which was able to detect if your taillights were on?

A way to monitor your taillight activity such as:

Let's say you have this tiny sensor which you stick to your taillight lens and, regardless of day or night or other headlights or external sources, the sensor could tell you if your taillights were working via a wireless signal.

Of course it would be even better if the sensor could tell when your brake lights or directionals came on too. I had a guy work on this for me once using a small light-sensitive "eye" normally used on laptop computers for detecting backlight, but it wasn't very reliable and easily messed up from external sources. At night and if it was positioned correctly it worked though. It would send the light activity back wirelessly to a box which mimicked the original source.

I always thought that the sensor should not operate on light-sensitive eyes but should detect the magnetic fields around the bulbs instead such as a hall sensor might do.

Robhoski@yahoo.com

2. Aug 7, 2007

### Danger

You could just bond fibre-optic cables into the lenses and run the other ends to the dash display.

3. Aug 7, 2007

### robhoski

Hmmmm... that take all the fun out of it

Sure you could but at what cost? The idea is for the device to be portable and temporary. You could also hardwire the system even cheaper but with the same results.

4. Aug 7, 2007

### Danger

Ah, you never said anything about 'temporary' or 'portable' in your first post.
Maybe you could get one of those back-up cameras and mount it facing forward with a fish-eye lens to scan the whole rear of the car. I suspect that it would have a differentiation problem in daylight as well, though, between actual signal lights and reflections.
I don't know anything about the Hall effect pickups that you mentioned. Is the magnetic field from a taillight bulb even detectable from outside the glass?

5. Aug 7, 2007

### robhoski

Yeah, your right, I didn't say portable or temporary. But the camera approach would be too costly. I'm thinking a micro sized sticky sensor, simple, small, and wireless - and a remote unit which mimics the activity of the taillight being monitored. Not an easy application to solve I know. Thanks again.
Robert

6. Aug 7, 2007

### chroot

Staff Emeritus
You wouldn't even need to use optics. All you'd need to do is measure the current through the appropriate wires under the dash.

- Warren

7. Aug 7, 2007

I had no idea that you could get things like that for cheaper than the camera rig ($150). In that case, to fulfill all of your requirements, how about just using regular photoresistors or photodiodes that are painted black all over except for the side that's in contact with the bulbs? You could glue them to the bulbs with a tiny dab of silicone sealant, which can easily be scraped off later. You might even be able to use just one transmitter/receiver unit that uses pulse modulation like a TV remote to differentiate which trigger is active and display it properly. edit: Just saw Chroot's post. If that can be done without physically assaulting the wires (as in stripping or cutting), it could work. One thing that always worries me about messing with any wiring in a modern car is the sensitivity of those damned computers. You could tap into a taillight circuit and find out that it's disabled your fuel pump. Last edited: Aug 7, 2007 8. Aug 7, 2007 ### chroot Staff Emeritus Again, it seems to me that a simple adapter that plugs into one of the wiring harnesses under the dash and measures current would be the easiest, fastest, and most reliable means of ensuring that the bulbs are lit. I suspect you're trying to build some kind of product that people can use to test their own lights without any help. It seems like borrowing ten seconds of a friend's or neighbor's time would be a more effective method than buying some crazy high-tech contraption that will sit in your garage for six months before being used again. - Warren 9. Aug 7, 2007 ### Danger Well... if that's the case, all he needs is a wall mirror. 10. Aug 7, 2007 ### chroot Staff Emeritus Another good point.$5 at IKEA. Hang it in your garage. Done.

- Warren

11. Aug 7, 2007

### mgb_phys

Or a carefully trained small child.
Assembly instructions are easier than anything from IKEA and the delivery time is less than the wait to get into an IKEA carpark.

ps. My new car has a warnign light on the dash to tell you if any bulbs have failed, but there is no light to tell you if the warning light has failed ?

12. Aug 7, 2007

### Danger

:rofl:....

13. Aug 7, 2007

### robhoski

As I stated before Warren ... not everything is immediately apparent. Good guess though on the checking your taillights gadget idea though. But if you must know I'll actually tell you this one. The actual application for the discussion was to determine the feasibility of creating a wireless taillight system for trailers, capers, boats,etc. I've experienced it many times that the trailer I had wanted to haul did not match my connection to my truck or the connector was faulty on either the truck or the trailer. However, my own taillights operated just fine. In such a case, if a person was to have an "emergency taillight kit" which operated by mimicking the towing vehicle's taillight activity, then you simply attach a small sensor to each light and place the remote taillight units on the boat or camper or car or whatever you are towing and off you go. If you step on the brake in your truck then the corresponding remote unit also reacts by becoming brighter. If you turn on the blinker, then the remote unit flashes also. Get it?

You seem like a smart guy Warren but very closed off to your creative side. I wish you well.
Robert

14. Aug 7, 2007

### chroot

Staff Emeritus
Except your trailer doesn't have a battery to power the lights. And if it does have a battery, it'll quickly get depleted, and you'll again need some kind of wires to charge it.

- Warren

15. Aug 7, 2007

### mgb_phys

I would build a standalone box that the trailer electrical connector plugged into. It could measure the resistance of each pair of wires to determine which had bulbs on ( or is there a standard for pinouts?).
It could then apply 12V and measure the change in resistance as the filament heated up to determine if a bulb was present and not simply a short.
It could also run the lights in a pre-determined test pattern to allow you to check them by eye.

16. Aug 7, 2007

### robhoski

There is an issue of speed and convenience involved. Consumers like products that are very intuitive. They don't want to make electrical connections. That was the idea behind a simple sticky sensor and corresponding remote taillight. Left and right respectively. As for the power source for the remote unit ... the low power consumption of LEDs make it feasible these days to run such an application. You could use a rechargeable batteries with the option to use regular bats if needed. Since it is for emergency use only the DOT regulations for brightness may not apply. Regardless, it is possible to create an LED array which is bright enough for taillights as they are already in use.

17. Aug 7, 2007

### chroot

Staff Emeritus
If customers have two choices that get the job done, one that's cheap, and one that's intuitive, guess which one they usually pick? You can go down the Pep-Boys and buy tail-lights on long wires that you can run back to your hitch.

It's a decent enough idea, but the tiny, sticky, wireless light sensors are a larger concern than you might imagine. They'll need some kind of a power supply, and it'll need to be substantial if you want them to continue working for the duration of a long trip.

- Warren

Last edited: Aug 7, 2007
18. Aug 7, 2007

### NoTime

For battery charging you could hook a generator to one of the trailer wheels.

19. Aug 7, 2007

### chroot

Staff Emeritus
Yeah, but this will add a hundred bucks to the trailer's cost (and add some maintenance requirements, too). Not a very elegant way to handle emergency situations. Especially when you consider that the justifcation for this little product is faulty wiring on trailers that have not been maintained well.

- Warren

20. Aug 7, 2007

### robhoski

Well at least the discussion has lightened. Yes sensors are costly until mass produced. I recently saw somewhere that video cameras were eventually going to be as easily applied as a postage stamp. Stick them to something and log into the IP address to see what's going on. Very interesting. If not invasive.