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Dug it out to trouble shoot and learn
Had to bump this as I decided to pull it off the shelf and start trouble shooting again, mostly just to teach myself and to see if I could really figure out on my own what the problem/issue was with this particular build.
Well, I found 3 things. I pulled all the chips and started from the beginning and went thru each step. Once I was at step 5, I noticed it wasn't working correctly and based on the old comments and help I started searching the board and found that C8 was incorrect, it was a 103 (10N) should have been a 101, changed it and now things were acting differently. I also found C20 was a 223, so yanked it and replaced with a correct cap (221). That changed how the voltage read for step 5, so now everything worked up to step 6, like before.
Now, I was at a stand still and pretty much went over the whole thing with a fine tooth comb and pulling what hair I have left out... Finally found the problem and really, how I over looked it in the first place, I will never know or understand. The problem was with U6 and U7 (along with the wrong caps)
I had purchased a tube of MC14538BCP (20 of them) and since I have never had an issue with a chip, I didnt think twice about these, looked at the numbers and good to go.....
WRONG WRONG WRONG......
Well, the problem was that in the tube of 20 chips, ten of them were NOT - MC14538BCP's, somehow, the other ten were (other half of tube) HCF4538BE's. When I looked at them they were correct (saw the ones on one end of the tube), when I opened them, I opened the tube from the other end and used 2 of the other chips....
Now to be honest, I haven't looked up the data sheet yet to see if they are compatible, but what I did do was install the correct chips to the board and continue testing and lo and behold, the dogon board works......
So much for being diligent and trying to be as thorough as possible.......
So, now I have another working minipulse (first build that went awry).....
Lets continue, I finished out the board, adjusted everything based on my copy of the build doc and now see an issue (which can be fixed with a resistor change I believe) with the sample pulse.
With probes on TP3 and TP5, the sample pulse is oddly in the wrong place (directly under main pulse, see pic), but check this out, when I adjust the delay pot from lowest setting to the half way point, it changes the sample pulse width from approx 12us to about 20us, as I continue to turn the delay pot all the way full clockwise from the half way point, the sample pulse width goes back to 12us... So from low setting (all the way counter clockwise) to high setting ( full clockwise) it goes from 12us to 20us at the half way point and then reverts backwards, back to 12us at full clockwise....
Anyone have an idea what may be causing the low to high to low on the reject delay pot adjustment?
Other than the issue above, the board is working as it should, detects a US nickel at 8 inches and my 14k gold ladies wedding band at 8 inches, a soda can at about 20 inches... kinda weird but hey, if it aint broke, dont F with it, isnt that what murphy supposedly said!!!
Finished board.
scope shot of sample pulse.
stretched out to see alignment.
Had to bump this as I decided to pull it off the shelf and start trouble shooting again, mostly just to teach myself and to see if I could really figure out on my own what the problem/issue was with this particular build.
Well, I found 3 things. I pulled all the chips and started from the beginning and went thru each step. Once I was at step 5, I noticed it wasn't working correctly and based on the old comments and help I started searching the board and found that C8 was incorrect, it was a 103 (10N) should have been a 101, changed it and now things were acting differently. I also found C20 was a 223, so yanked it and replaced with a correct cap (221). That changed how the voltage read for step 5, so now everything worked up to step 6, like before.
Now, I was at a stand still and pretty much went over the whole thing with a fine tooth comb and pulling what hair I have left out... Finally found the problem and really, how I over looked it in the first place, I will never know or understand. The problem was with U6 and U7 (along with the wrong caps)
I had purchased a tube of MC14538BCP (20 of them) and since I have never had an issue with a chip, I didnt think twice about these, looked at the numbers and good to go.....
WRONG WRONG WRONG......
Well, the problem was that in the tube of 20 chips, ten of them were NOT - MC14538BCP's, somehow, the other ten were (other half of tube) HCF4538BE's. When I looked at them they were correct (saw the ones on one end of the tube), when I opened them, I opened the tube from the other end and used 2 of the other chips....
Now to be honest, I haven't looked up the data sheet yet to see if they are compatible, but what I did do was install the correct chips to the board and continue testing and lo and behold, the dogon board works......
So much for being diligent and trying to be as thorough as possible.......
So, now I have another working minipulse (first build that went awry).....
Lets continue, I finished out the board, adjusted everything based on my copy of the build doc and now see an issue (which can be fixed with a resistor change I believe) with the sample pulse.
With probes on TP3 and TP5, the sample pulse is oddly in the wrong place (directly under main pulse, see pic), but check this out, when I adjust the delay pot from lowest setting to the half way point, it changes the sample pulse width from approx 12us to about 20us, as I continue to turn the delay pot all the way full clockwise from the half way point, the sample pulse width goes back to 12us... So from low setting (all the way counter clockwise) to high setting ( full clockwise) it goes from 12us to 20us at the half way point and then reverts backwards, back to 12us at full clockwise....
Anyone have an idea what may be causing the low to high to low on the reject delay pot adjustment?
Other than the issue above, the board is working as it should, detects a US nickel at 8 inches and my 14k gold ladies wedding band at 8 inches, a soda can at about 20 inches... kinda weird but hey, if it aint broke, dont F with it, isnt that what murphy supposedly said!!!
Finished board.
scope shot of sample pulse.
stretched out to see alignment.
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