Need help with homemade sensor

Hank S

My son created a sensor by taking apart his metal detector.· At one time, he actually got the board to detect a siganl from the metal detector and respond.· He ran a lead from the LED on the detector to a pin on the board of education (BOE), and to my suprise got it working.· Unfortunately, he puurchased a smaller, lighter-weight metal detector so that if could be carried by the robot, and has not been able to replicate the success with the earlier detector.

With the new metal detector he has to run a lead from the speaker to the BOE since there is no LED.· When the detecor picks up a metal object it sends a chiping sound to the speakder.· The chip is not picking up any change in voltage when the detector sends a signal.· We don't know why, other than we're doing something wrong.· Although he said that he got things working (with the first detector)·using only one lead from the LED, we have not been able to replicate the configuration using one or two wires for hot or cold config.

Can anyone suggest a configuration, taking us from the speaker, to the BOD using one or two wires.

thank you.

Mike Green

Unfortunately, it's a little more complicated using the sound output for a speaker rather than the on/off signal from an LED. A Stamp can directly detect the signal to the LED. It can't do that with the audio from the speaker. Here's one audio detector meant to be used with a little microphone to actually detect the sound rather than the electrical signal: www.seattlerobotics.org/encoder/200003/larryb.html.
Here's another: www.reconnsworld.com/audio_electretamp.html.

Please do not post the same request on more than one forum. It's against forum rules. You can delete the other one by clicking on the X in the right upper corner of your original posting.

Franklin

Could you give us the model number and manufacturer of the detector in question and how your son is hooking it up and attach the code he is using to try to detect the signal?
Thanks

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Stephen

Beau Schwabe

Can you post a schematic of what he currently has tried with the speaker hookup to the BOE? If he is using the same power supply for the detector that he is using for the BOE, then it might be a simple matter of reversing the polarity from the speaker connection to the BOE. I do hope that he is using some sort of current limiting resistor between the speaker and the BOE however.

Also, can you post the code he is using to attempt to read a signal?


Another thought... the speaker might have a DC bias on it that could be affecting the detectable voltage level... One way to overcome this is to use an audio isolation transformer (Radio Shack used to sell them cheap)
a second method is to use a capacitor to block any DC bias in the audio signal.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe

IC Layout Engineer
Parallax, Inc.

steve_b

Got an oscilloscope?
If you took the wires right off of the speaker, then I'd suspect there probably isn't an DC bias (speakers don't usually like that).

My guess is there probably isn't enough voltage to do much with it.


Here's a couple of circuit links to try....
www.reconnsworld.com/audio_electretamp.html
www.reconnsworld.com/audio_sounddetectlatch.html

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
<FONT>Steve



What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!

Paul Baker

Duplicate messages in other forums have been deleted for violating forum rules against cross-posting.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Paul Baker
Propeller Applications Engineer

Parallax, Inc.

manxstamp

A Thai company, INEX, who make basic stamp clones for their local·educational market, sells a small (2x1 inch) digital metal detector. I have one for use with their Sci-Box, a 'school' basic stamp clone educational board.

see http://www.inexglobal.com/products.php?type=addon&cat=sensors&model=zx-metal

This may be what you need for a robot as it weighs very little. However, you will need to check that its sensitivity is what you require. Connecting it is simple as detection gives a change from logic 1 to logic 0 on the output. The supplied cable can easily be adapted to plug into any connector.

John


▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

---

Manxstamp,
Isle of Man, British Isles