XR71 Operation Help

		Quote:			Posted by ameen
	Hello We have built one, but it does not work. I hear a voice when running and then press reboot and the sound disappears and the device is not sensitive to the metals. Is the resistance side of 740 should be 1 watt. ne 556 heat And also a warm 740 Can you help me Forgive me for my bad English

Please use the schematic I posted a few days ago . If you have less than 2.0 ohms on your search coil the IRF740 will get hot . You need to wind a new search coil try with at least 2.9 ohms dc
HH........Eugene

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		Quote:			Posted by raff33
	hi Eugene,  but the schematic you posted is for double side not for single side........ Regards...........Raff33

You are correct , makes sense now !!!!  The single side PCB and double side PCB use different schematics but they are not too much different , just enough to give everyone a slight headache . I will go back and make sure that the right schematic goes to the right pcb board . The best , most accurate , most used schematic is the one I just posted above . And the single side PCB board is the easiest to make .         The Delta Pulse Metal Detector project is the most built and most popular in the world !!!
HH............Eugene

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		Quote:			Posted by raff33
	hi Eugene , now i inderstand ........  what the resistance prefer for search coil 1m*1m .......please  thanks for helping

Remember sometimes on very large diameter search coils you may have to add a small value resistor in series with the coil to keep the total resistance above 2.5 ohms !!! I will look up the specs you need again for the 1 meter by 1 meter coil . I posted it already on this forum a few times plus I know I have alzheimers at 53 years old !!  
HH........Eugene

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		Quote:			Posted by steaua581
	Hello Eugene, I have finished too delta Pulse but im getting also poor detecting...i have used the single side PCB scheme all functions all things acording to your specs but still poor detecting..The Delta runs good but it seems to me instabil.The only thing instead LF357  i used  LF356 .Is that the problem?.. My coil is 40 Cm @ 23 Turns , 0,5 wire. I have included a pic of my PCB... Whats wrong? Regards Marius

LF357 and LF356 should have the same gain , only LF356 is a bit more noisy . You need to check signal at P4 [20k] potentiometer before jfet TLO62 opamp . You are loosing signal , there should be your problem . If you have an oscilloscope you can fix it very fast !!!!
HH.........Eugene

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Hi Eugene,
it is ok now ,with R5 is 680 ohm 1 watt . And R6 is 1 k ohm , changed C30 10.000 uf by 4,700 uf  . Seach coil 28cm diameter ,31tr with 3,5 ohms dc resistance . my DP can detect in air 1 euro at 25cm and a canet PEPSI 250ml at 70 cm ;many thanks........
but why it is not stable , i can't find lf357 i replace with TL071, T1: IRF840 , do you think the probleme is 23,24,25,26  (5%)...............? many thanks again

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