Need advice: Metal detector with stm32f103

What are you developing?
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Pito
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Re: Need advice: Metal detector with stm32f103

Post by Pito » Sat Mar 18, 2017 3:31 pm

A 7805 TO-220 can source 1A or more :) The 7805 TO-92 about 150mA.
It may happen the current pulse into the coil is so large that your battery drops down to nil volts :)
Try to switch off the MM from the metal detector circuit and source the MM from USB only. Have a look at the PB1. It must give you a 3.3V pulse.
What O'scope do you use?
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asen0v
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Re: Need advice: Metal detector with stm32f103

Post by asen0v » Sat Mar 18, 2017 3:40 pm

Try to switch off the MM form the metal detector and source the MM from USB. Have a look at the PB1. It must give you 3.3V pulse.
I did it. There is no problem from the USB. I also tried from other power supply and still there is no problem. The pulses are 3.3V. The problem occurs only when I feed it from the 7805 of the metal detector's board.
What Oscope do you use?
It is a cheap "Instrustar ISDS205A" Chinese USB scope. I use it for two years and never had any problems with it.

asen0v
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Re: Need advice: Metal detector with stm32f103

Post by asen0v » Sat Mar 18, 2017 3:49 pm

Found the reason. I connected the scope GND to a wrong place :D
Now I will test the metal detector board and will write again if there is some progress.
Pito, thank you again for the answers!

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Pito
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Re: Need advice: Metal detector with stm32f103

Post by Pito » Sat Mar 18, 2017 4:00 pm

How sensitive is the detector? I am looking for a MDet which can find a coin 10m deep in the soil :)
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asen0v
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Re: Need advice: Metal detector with stm32f103

Post by asen0v » Sat Mar 18, 2017 4:08 pm

Pito, unfortunatelly such a beast does not exist :))) The deepest and best detectors in the world are the Australian "Minelab" detectors, but even their 20000$ model detects a big coin 60 centimeters in the soil.
The last time I made DIY metal detector it was 30 centimeters deep for a 22mm coin. Not bad for a homemade machine. But it was not DSP and was a lot easyer to do. This time it is hard :)

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Pito
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Re: Need advice: Metal detector with stm32f103

Post by Pito » Sat Mar 18, 2017 4:13 pm

With an 1GW Xray laser pulse and liquid helium cooled detector you must detect a coin 10m deep in the soil :)
The only issue with such setup would be the digging into such deepness - quite an effort :)
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asen0v
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Re: Need advice: Metal detector with stm32f103

Post by asen0v » Sat Mar 18, 2017 5:41 pm

So, the results with 20cm coil:
1€ coin - 17cm.
Big gold ring - 21cm.

Tomorow I will play with the damping resistor, the coil and the code and hope to double the depth. Alwso the MM and opamp are put on a socked and not dyrectly soldered to the board. When I solder them I hope to get less noice and better result.

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Pito
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Re: Need advice: Metal detector with stm32f103

Post by Pito » Sat Mar 18, 2017 6:32 pm

In the air?
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asen0v
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Re: Need advice: Metal detector with stm32f103

Post by asen0v » Sat Mar 18, 2017 7:46 pm

No, in the soil of my back garden.

zmemw16
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Re: Need advice: Metal detector with stm32f103

Post by zmemw16 » Sat Mar 18, 2017 8:41 pm

if you dig the coins in, will disturbed soil affect the test?
or do you stamp the soil back down ?
srp

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