Greetings again,
Since 6666 expressed an interest in the circuit that I ended up with for my homemade PI I will what I came up with. I will also pass along some of the thoughts behind what I did. This was a learning process for me and some of my thinking may be off base and some of you might be able to show me the error of my ways. I would appreciate any inputs to that effect. Since I have been field testing my detector every chance I get, I had it out for a bit this weekend. I didn't have a lot of time but I did spend about 45 minutes hunting in an old church play area in a small mountain town. I have attached a photo of the finds. It is only of the good stuff and does not include the wire, nails, bobby pins, paper clips and other iron treasures. The small gold ring has a little diamond in it at the center. It was found about 3 1/2 to 4 inch's in the ground. I was using the 8" coil and it had a nice clear signal. The ground up there has a fair amount of mineralization in it. Both my Xterra 705 and my AT Pro bare this out. The AT Pro read the ground at 92 out of a max of 99. My front yard is not a whole lot better, it reads 85 ot 87. The detector performed very well under that type of ground condition. I also included a closer shot of the control box so you can see the controls that ended up on the front panel. I have attached the schematic of the power supply for everybodys review. There is nothing earth shaking about the design.
I used three supplies in the machine, a -12V to -15V battery supply, a +5V and a -5V supply. The 12V comes from 8 AA batteries, and I have a 14.8V, 4 cell Lipo battery that can also be used. To generate the +5V supply, is used a bipolar NE555 timer running at about 20 KHz. The 20KHz frequency was selected for 2 reasons, less ripple and since bipolar NE555s can generate fairly large current spikes on the power supply, if there is any left after decoupling and filtering the 20 KHz will help to keep it from being heard in the output audio. The output of the NE555 drives a voltage doubler circuit to make sure that there is plenty of voltage for the LM7805 +5V regulator. The -5V is taken directly off the -12V to -15V battery supply using a LM7905 -5V regulator. Diode across the 3.3k resistor in the timing circuit on the NE555 is to separate the charge path and the discharge path and give a 50/50 duty cycle square wave output to the voltage doubler. The NE555 timer must be a bipolar device. The Cmos version does not have enough current drive to drive the voltage doubler.
Well there is my thoughts on the power supply, I will get into the rest of it next time.
God Bless and HH!
Smitty II
Since 6666 expressed an interest in the circuit that I ended up with for my homemade PI I will what I came up with. I will also pass along some of the thoughts behind what I did. This was a learning process for me and some of my thinking may be off base and some of you might be able to show me the error of my ways. I would appreciate any inputs to that effect. Since I have been field testing my detector every chance I get, I had it out for a bit this weekend. I didn't have a lot of time but I did spend about 45 minutes hunting in an old church play area in a small mountain town. I have attached a photo of the finds. It is only of the good stuff and does not include the wire, nails, bobby pins, paper clips and other iron treasures. The small gold ring has a little diamond in it at the center. It was found about 3 1/2 to 4 inch's in the ground. I was using the 8" coil and it had a nice clear signal. The ground up there has a fair amount of mineralization in it. Both my Xterra 705 and my AT Pro bare this out. The AT Pro read the ground at 92 out of a max of 99. My front yard is not a whole lot better, it reads 85 ot 87. The detector performed very well under that type of ground condition. I also included a closer shot of the control box so you can see the controls that ended up on the front panel. I have attached the schematic of the power supply for everybodys review. There is nothing earth shaking about the design.
I used three supplies in the machine, a -12V to -15V battery supply, a +5V and a -5V supply. The 12V comes from 8 AA batteries, and I have a 14.8V, 4 cell Lipo battery that can also be used. To generate the +5V supply, is used a bipolar NE555 timer running at about 20 KHz. The 20KHz frequency was selected for 2 reasons, less ripple and since bipolar NE555s can generate fairly large current spikes on the power supply, if there is any left after decoupling and filtering the 20 KHz will help to keep it from being heard in the output audio. The output of the NE555 drives a voltage doubler circuit to make sure that there is plenty of voltage for the LM7805 +5V regulator. The -5V is taken directly off the -12V to -15V battery supply using a LM7905 -5V regulator. Diode across the 3.3k resistor in the timing circuit on the NE555 is to separate the charge path and the discharge path and give a 50/50 duty cycle square wave output to the voltage doubler. The NE555 timer must be a bipolar device. The Cmos version does not have enough current drive to drive the voltage doubler.
Well there is my thoughts on the power supply, I will get into the rest of it next time.
God Bless and HH!
Smitty II