Short range remote

[EPL]

Hi everyone, I'm new to the forum and I have an application where I can't seem to find the right product for the job. I need to activate some doors remotely from a mobile equipment. In some cases there may be doors that are within 50ft of each other and I only want the door that is closest to me to activate. This is a safety issue. We have been testing some infrared remotes but the ones we have tested are too sensitive to regular light and they get triggered from the miners head lamps. This is unacceptable. Also some flashing lights on the vehicles are also triggering the sensors as well. I deally I would like to find a RF style discrete transmitter/receiver with a range of 20-25ft. Everything I've come accross is typically 300ft or more. Any sugestions? Thanks, Eric

[TimWilborne]

Is the same transmitter to operate all of the doors? It there will be individual transmitters for each door then this may sound simple but have you thought about garage door openers? I have seen them in plants doing exactly this. You can set the frequencies to keep them from interfering. Most of the remotes that have the safety circuits to keep transmitters and receivers from interfering with one another are going to be in the 300' plus range and be much more expensive. You are going to have a hard time if you want to have a single transmitter operate all the doors. Have you thought about ferrite magnets (I think that is the technical term for huge prox switches like traffic lights have). Or if you don't want to dig up the floor, how about safety mats. You can run fork lifts over them and I have heard of people using these to open doors but I have never seen that.

[EPL]

Yes the one transmitter is to open all the doors. Here's a bit more details about the application: We have trucks travelling in an underground mine. There are multiple ventilation doors and doors for orepasses. The operator is to be able to open/close these doors from within his cab. Many trucks will be used and there are multiple doors, some of which are really close to one another. Every truck will have a transmitter that can control all the doors which would have a receiver set at one frequency for all. My original idea was to use 4 separate buttons color coded with some signs on the doors that displays the color code of this door. There would never be more than 4 doors within range and the operator would simply need to press the right button for the door he wants to activate. Some people are still concerned that it would still be too easy for the operator to hit the wrong button and activate the wrong door. If you can think of a different technology or other ideas to use the current technology, I'll take any ideas right now and try to make sense of it. Also, this is an extremely harsh environment. We would not be able to have any type of sensor on the floor or even a mat. It wouldn't last a day! The floor gets scraped with a plow to keep the roadbed level. Thanks for the help. Eric

[TimWilborne]

Oh now you tell me it's a mine. Never knew they used things like that down there. I used to build control panels for mining equipment. I don't think IR would be a good thing because build up on the reciever. You are probably correct looking at RF as far as remotes go. How many pieces of equipment are we talking about being able to open the same door? How many doors are we talking about that will be line of sight of each other?

[Camel]

Have you looked into RFID? We have a simillar application where we sense a yard dog (big truck) going through a door. The doors are less than 20 ft apart and there is no crossing of signals. The version of RFID we have actually has doppler radar and can determine target speed and direction. As a matter of fact, with the RFID setup you would actually be able to tell exactly which truck is trying to go through which door at what time because the number stored on the tag that the reader senses is unique on a tag by tag basis (which is also reprogrammable). We mounted our RFID readers above the doors, and the RFID tags on the roof of the trucks. We used Pepperl+Fuchs RFID tags and readers. Edited April 6, 2006 by Camel

[DanW]

I'm not sure what the range of a residential garage door opener is, 50 feet maybe? (I don't have one, so I can't test it). Bluetooth is a short range RF, probably less than 100 foot. Dan

[rajsiyer]

Hi guys, I've been thinking of this situation... Perhaps the best /simplest/cheapest way to go about it seems to use Ultrasonic transducers. More exactly a matched transmitter receiver pair(30 or 40Khz). The doors all must have a receiver and each truck has a simple one button transmitter device. The truck appproaching the closed hits a single button and the ultrasound pulse activates the opening mechanism, perhaps all wired to PLC outputs. The logic in the PLC would ensure all safety interlocks. It may not be a bad idea to retrofit the TXR and RXR of existing IR/RF circuits (such as garage door control devices). And transducer pairs are quite inexpensive even here in India! Ultrasonic works well in even strong sunlight and the transmitter is robust and can tolerate a lot of muck. Above all, rugged environments like what you describe must not have more complexity as may result out of multiple frequencies, sophisticated electronics etc... Best of luck Raj S. Iyer