Arduino metal detector shield?

[dingbatca]

Looking to build a simple VLF/IB metal detector. I plan to use an Arduino for all the signal comparison/processing. I would like to put all the hardware on an Arduino shield. Keep the whole project open and free, hardware/code.

I am good with code logic and algorithms, but suck at designing hardware.

I need help with two circuits (Not sure on the power, or the amperage):
1) Amp circuit to take the signal generated by the Arduino (5Hz~64kHz square wave) and pump it up to 200~1000ma, for the TX coil.
2) A opamp to take the signal from the RX coil from 0.001~50mv to 0.1~5V for the analog in on the Arduino.

Lets start simple. I would like to detect the difference between open air, and the metal hood of my car at 1in away

Is this a sound idea? Am I going about this correct?

[Qiaozhi]

Looking to build a simple VLF/IB metal detector. I plan to use an Arduino for all the signal comparison/processing. I would like to put all the hardware on an Arduino shield. Keep the whole project open and free, hardware/code.

I am good with code logic and algorithms, but suck at designing hardware.

I need help with two circuits (Not sure on the power, or the amperage):
1) Amp circuit to take the signal generated by the Arduino (5Hz~64kHz square wave) and pump it up to 200~1000ma, for the TX coil.
2) A opamp to take the signal from the RX coil from 0.001~50mv to 0.1~5V for the analog in on the Arduino.

Lets start simple. I would like to detect the difference between open air, and the metal hood of my car at 1in away

Is this a sound idea? Am I going about this correct?

Welcome to Geotech.

My advise would be to use a commercial coil in your project (at least for the first stage) otherwise you'll probably fall at the first fence.
Have a look at the Tesoro Golden Sabre Lite (TGSL) ->
http://www.geotech1.com/forums/showthread.php?t=15710
Your quickest route to success IMHO would be to build the TX oscillator circuit and RX pre-amp from the TGSL, and to use one of their coils with the 5-pin plug. These coils come up on eBay quite frequently.

Alternatively you could get some ideas from the projects section ->
http://www.geotech1.com/cgi-bin/page...e=projects.dat

Good luck!

[ApBerg]

Hello dingbatca,

Advice from Qiaozhi is o.k. but you can also look here for the schematic from the Tesoro lobo or diablo , there is a nice transmitter and receive circuit in it
Go for 18-19 kHz, but 200-1000mA (1 AMP) is a to much

Regards

Ap

[Qiaozhi]

Hello dingbatca,

Advice from Qiaozhi is o.k. but you can also look here for the schematic from the Tesoro lobo or diablo , there is a nice transmitter and receive circuit in it
Go for 18-19 kHz, but 200-1000mA (1 AMP) is a to much

Regards

Ap

I agree. For this particular application, where the coil is to be driven from a micro-controller, then the Lobo or Diablo would be good choices.
Here are the schematics ->

[dingbatca]

Wow, so much good info! Thank you.

So I walked through the 4 different schematics, and here is what I got. Am I close?

[dingbatca]

Some more thoughts as I look through the schematics.

TX Amp: All 4 use some from of a PNP transistor as the amp. Most are using the 2n2907a with the exception of the heathkit which uses a MPSA55 transistor. Easy for me to chose a amp circuit.

TX signal gen: I see what looks like a flip flop, and three variations based on the cd4024. I think I drive the TX signal generation circuit with the Arduino. Any objections?

RX opamp: I see two different approaches, but I think the dual LS204 will give me the best results.

Sound like a good plan?

[WM6]

. I think I drive the TX signal generation circuit with the Arduino. Any objections?

Obligatory. Why else would use Arduino? All signal processing to fall into Arduino.

Tesoro front modules are good choice, I think.

Wish you full success!

[dingbatca]

I picked up a cheap search coil off ebay to play with/hack apart and understand.
"Bounty Hunter 10 inch Magnum Search Coil"

[dingbatca]

Slight change of plans.
Using the Arduino as a signal generator.

The RX, and control signal(TX), will get digitized and pass to my Android phone using bluetooth. Also plan to pass instructions/setup info from the phone to Arduino board. Things like frequency and wave/pulse shape.

The Arduino does not have enough power to do full digital signal processing. My Android phone... 1GHz CPU + sound card + nice day light viewable screen.... This could work out very well.

[WM6]

Slight change of plans.
Using the Arduino as a signal generator.

The RX, and control signal(TX), will get digitized and pass to my Android phone using bluetooth. Also plan to pass instructions/setup info from the phone to Arduino board. Things like frequency and wave/pulse shape.

The Arduino does not have enough power to do full digital signal processing. My Android phone... 1GHz CPU + sound card + nice day light viewable screen.... This could work out very well.

Big and interesting project with Android included, I hope you finish it as you plan. Waiting for your progress reports.

[msysta]

When planning to use BT as media please do mind the delay. In theory it works but think about the search situation. You want to have real time response when you swing the coil.

[dingbatca]

I have hit my first snag... Am I am sure it will not be my last.

Lets use a 32KHz sign wave to the TX coil (32,000Hz)
I want 100ish sample per cycle. 32,000*100 = 3,200,000 sample
Lets state I am using a 10-bit ADC. So each value will need to be stored in an unsigned integer (2 bytes, or 16 bits).

Number of sample * bits of data.
3,200,000 * 16 = 51,200,000, and the max speed of a bluetooth connection is 115,200 bits/s....

Ideas?

[Qiaozhi]

I have hit my first snag... Am I am sure it will not be my last.

Lets use a 32KHz sign wave to the TX coil (32,000Hz)
I want 100ish sample per cycle. 32,000*100 = 3,200,000 sample
Lets state I am using a 10-bit ADC. So each value will need to be stored in an unsigned integer (2 bytes, or 16 bits).

Number of sample * bits of data.
3,200,000 * 16 = 51,200,000, and the max speed of a bluetooth connection is 115,200 bits/s....

Ideas?

The TX frequency you have chosen is too high for a VLF. You should stay within the range of 7kHz to 14kHz for your experiments. I would suggest using either 10 to 12kHz as a starting point.

[dingbatca]

30KHz was me goofing off. Just like 3KHz.
3,000*100 = 320,000 * 16 = 5,120,000 which is still WAY past 115,200, the max speed of bluetooth.

[dingbatca]

Still planning on the Arduino/bluetooth setup. Looked into the delay time on bluetooth... I can deal with 3~15ms, this is a metal detector, not a super computer. :-)

1) Problem: using a 16mhz CPU
2) Problem: trying to RX/TX with a 16mhz CPU
3) Problem: trying to send all raw data through a slow (bluetooth) interface

1) Fix: Use two 16mhz CPUs :-)
2) Fix: Get a fast ADC and only sample 32 times a cycle, and use a dedicated CPU.
3) Fix: Dont send all raw data. Send the sum of each cycle, not all 32 samples.

Ordered in the ADC and DAC's today. Hope to have them later this week to start testing.

Once I prove that I can both generate, and sample a wave form, I will order in the 2n2907a, and the LS204.