mikezang Posted October 21, 2013 Posted October 21, 2013 I don't know why, and I found all my RCX touch sensors don't longer work just moment, and I tried to use bricxCC and brickOS to test them, they are never on even I pressed yellow button on touch sensor. Does anyone have similar experience? do I have to open them to fix? Thanks a lot! Quote
mikezang Posted October 21, 2013 Author Posted October 21, 2013 I opened damaged touch sensor, but I don't know where has problems... Quote
Blakbird Posted October 21, 2013 Posted October 21, 2013 Those old touch sensors seem very unreliable. Many of mine also no longer work. I suspect internal corrosion. Keep in mind that this is not really anything as fancy as a "touch sensor", it is just a momentary switch. When it is pushed, it should make contact and close the circuit. Otherwise the circuit is open. There are no electronics involved. From that point of view, there is really nothing that can go wrong with it other than broken or corroded contacts. Quote
mikezang Posted October 21, 2013 Author Posted October 21, 2013 Those old touch sensors seem very unreliable. Many of mine also no longer work. I suspect internal corrosion. Keep in mind that this is not really anything as fancy as a "touch sensor", it is just a momentary switch. When it is pushed, it should make contact and close the circuit. Otherwise the circuit is open. There are no electronics involved. From that point of view, there is really nothing that can go wrong with it other than broken or corroded contacts. Thanks for your message, I just was in panic because I need those old touch sensors in my projects! Like you said, maybe the rubber is getting thin so that it can't touch to internal wire, I have a idea to put a thin metal on rubber, this might fix touch sensor, anyway I will try it. Quote
DrJB Posted October 21, 2013 Posted October 21, 2013 Rather than testing them on the RCX, I would try them first on a power supply (battery box) + motor (or light). Press button and see what happens .... Normally doing so will short the two leads (close the circuit) and the motor will stop running and light turn off. If that does nothing, then your sensor is damaged. If they work, then something is wrong with your RCX ... Quote
mikezang Posted October 21, 2013 Author Posted October 21, 2013 Rather than testing them on the RCX, I would try them first on a power supply (battery box) + motor (or light). Press button and see what happens .... Normally doing so will short the two leads (close the circuit) and the motor will stop running and light turn off. If that does nothing, then your sensor is damaged. If they work, then something is wrong with your RCX ... Maybe I have to modify title of this post, because I found one my touch sensor(1/20) is ok, so I can say my RCX is no problems. Anyway, thanks for your idea. Quote
Carsten Svendsen Posted October 21, 2013 Posted October 21, 2013 I've got 6 blue of these old touchsensors from the old Cybermasters set and all of them still works when I tested them on my NXT. Quote
pmichiel Posted October 23, 2013 Posted October 23, 2013 (edited) All of my 10+ year old RCX touch sensors still work fine. I'm wondering if using them as a switch for a motor like Blakbird DrJB suggested isn't precisely what's caused them to fry in the first place. Per Philo's motor characteristics page, a typical motor from the RCX age (43362) can draw up to 340 mA current (stalled), at the 7V the RCX output port produces. The RCX sensor ports give only 5V, and "The maximum current that may be drawn by “unpowered” sensors is 0.5mA" (source) Edited October 23, 2013 by pmichiel Quote
Philo Posted October 23, 2013 Posted October 23, 2013 Rather than testing them on the RCX, I would try them first on a power supply (battery box) + motor (or light). Press button and see what happens .... Normally doing so will short the two leads (close the circuit) and the motor will stop running and light turn off. If that does nothing, then your sensor is damaged. If they work, then something is wrong with your RCX ... No, that won't work! RCX touch sensors have an internal resiatance around 500 Ohm, much too high to light a lamp or allow a motor to run (and as pmichiel suggested, you might even fry your sensor, burning the conductive rubber!) I just tested 10 RCX sensors, all of them work fine. Quote
Blakbird Posted October 23, 2013 Posted October 23, 2013 All of my 10+ year old RCX touch sensors still work fine. I'm wondering if using them as a switch for a motor like Blakbird suggested isn't precisely what's caused them to fry in the first place. I didn't suggest using them as a switch for a motor. In fact, the only touch sensors I have are those that came with the 8479 barcode truck. They both stopped working, I replaced them several years ago, and they have since stopped working again. Quote
pmichiel Posted October 23, 2013 Posted October 23, 2013 I didn't suggest using them as a switch for a motor. In fact, the only touch sensors I have are those that came with the 8479 barcode truck. They both stopped working, I replaced them several years ago, and they have since stopped working again. Oops - I need to learn to quote. I was referring to DrJB's post! Sorry Quote
aol000xw Posted October 23, 2013 Posted October 23, 2013 The only reason I see for the sensors to stop working are corrossion and rust, nothing that can't be solved with some sandpaper. The amount of metal in the sensor probably can handle a few amps without even getting warm. Quote
Philo Posted October 23, 2013 Posted October 23, 2013 The amount of metal in the sensor probably can handle a few amps without even getting warm. NO!!! contact is not done with metal but with relatively high resistivity conductive rubber. Note that NXT touch sensor uses a true metal-to-metal switch, but there is a 2.2kOhm resistor in series... Quote
DrJB Posted October 23, 2013 Posted October 23, 2013 (edited) No, that won't work! RCX touch sensors have an internal resiatance around 500 Ohm, much too high to light a lamp or allow a motor to run (and as pmichiel suggested, you might even fry your sensor, burning the conductive rubber!) I just tested 10 RCX sensors, all of them work fine. Enlightening as always Philo ... Thank You! Will go home and check my 20+ sensors tonight ... with an RCX of course. Edited October 23, 2013 by DrJB Quote
Blakbird Posted October 23, 2013 Posted October 23, 2013 NO!!! contact is not done with metal but with relatively high resistivity conductive rubber. Note that NXT touch sensor uses a true metal-to-metal switch, but there is a 2.2kOhm resistor in series... Does that imply that perhaps the conductive broke down over time due to thermal cycling? If so, the switches may be very hard to repair. If I were to alter the switches to use direct metal-to-metal contact with minimal resistance, could it damage my electronics? Quote
aol000xw Posted October 23, 2013 Posted October 23, 2013 NO!!! contact is not done with metal but with relatively high resistivity conductive rubber. Note that NXT touch sensor uses a true metal-to-metal switch, but there is a 2.2kOhm resistor in series... I thougth it was not necessary to put the resistor, there was something about that and multiplexing the sensors... but I barely remember that so I guess I am wrong, anyways good to know, thank you. Quote
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