Rev A - Stuck in step 7

[diegogeid]

Yeah I figured it was odd, I'll wait for the oscilloscope to do the proper readings, thank you very much for your patience!

[green]

I would use my scope over the voltmeter to trouble shoot the problem. If no scope, a DC meter reading might define the problem. The outputs of U4 should be either -5v or 0v. If the output is high 5% of the time, should get a reading .95*-5v supply= -4.75v. If chip is bad and floating at some value the voltmeter won't help. -5v on pins 6,8,10 and 12 suggests U4 pin14 isn't at zero volts, U4 no good, C7 bad or others. What is the DC volts on U4 pins 4 and 5?

[kt315]

hung chang 3502, do you think it will serve?
---
good choice. 20mHz enough for this schematic.

[diegogeid]

Dc Volts on pin 4 of u4 is -4.82 and -0.84 on pin 5

[green]

Dc Volts on pin 4 of u4 is -4.82 and -0.84 on pin 5

Disconnect sample delay pot and remove jumper. Connect pin 5 to -5v, pin 6 should read 0v. Maybe a short between pins 6 and 7 if pin 6 doesn't go to 0v.

A scope does make it a lot easier to trouble shoot. With a voltmeter you have to assume digital logic is high or low when it should be.

[6666]

Looking at the picture of the PCB, R1 the coil damping resistor is not installed, this thing would be ringing , use pcb pins to mount R1.

[diegogeid]

Green, yes, when I short pin 5 with -5v, pin 6 goes to 0V rather than "-0.something"
6666, the damping resistor is installed on the test coil since I'm not working with the final coil, in fact I'd like to build different coils so I can change them on different occations, the manual suggested I can install the damping resistor across the leads of the coil

[green]

You have a good example where a scope would make it alot easier. -5v on pins 6,8,10 and 12 suggests neither of the one shots is being triggered. -.84v on pin5 suggests that one shot should be triggered and pin 6 should go high causing a reading of less than -5v supply on pin6. Will be interesting to see what the scope shows us.

[diegogeid]

Hi guys, today I received the scope, here you have the readings I got from u4, sorry for the blurry ones, if you need me to take some reading in particular, just say it. Al voltages are referenced to board ground. In case you can't see the settings, are: 1 volt/div, dc coupled, and time/div .5ms
scope settings: https://imgur.com/efj9qFZ
Not connected: https://imgur.com/cBLE9k1
pin 1:https://imgur.com/msKGQJs
pin 2:https://imgur.com/XUYYvnS
pin 3:https://imgur.com/NpSOvd1
pin 4:https://imgur.com/K5qQ1IR
pin 5:https://imgur.com/plJnpOz
pin 6:https://imgur.com/pgnS8HG
pin 7:https://imgur.com/4SgtyM2
pin 8:https://imgur.com/rSrzLYw
pin 9:https://imgur.com/lOerauT
pin 10:https://imgur.com/JawAyBn
pin 11:https://imgur.com/sZkiOg2
pin 12:https://imgur.com/Wm8wZmc
pin 13:https://imgur.com/Itys1bh
pin 14:https://imgur.com/lC7w8PX

[green]

Hi guys, today I received the scope, here you have the readings I got from u4, sorry for the blurry ones, if you need me to take some reading in particular, just say it. Al voltages are referenced to board ground. In case you can't see the settings, are: 1 volt/div, dc coupled, and time/div .5ms
scope settings: https://imgur.com/efj9qFZ
Not connected: https://imgur.com/cBLE9k1
pin 1:https://imgur.com/msKGQJs
pin 2:https://imgur.com/XUYYvnS
pin 3:https://imgur.com/NpSOvd1
pin 4:https://imgur.com/K5qQ1IR
pin 5:https://imgur.com/plJnpOz
pin 6:https://imgur.com/pgnS8HG
pin 7:https://imgur.com/4SgtyM2
pin 8:https://imgur.com/rSrzLYw
pin 9:https://imgur.com/lOerauT
pin 10:https://imgur.com/JawAyBn
pin 11:https://imgur.com/sZkiOg2
pin 12:https://imgur.com/Wm8wZmc
pin 13:https://imgur.com/Itys1bh
pin 14:https://imgur.com/lC7w8PX

Green, yes, when I short pin 5 with -5v, pin 6 goes to 0V rather than "-0.something" (reply 22)

Pin 5 goes to -5 in your scope pictures but pin 6 doesn't go to 0v in scope picture(it should). Pins 2 and 3 aren't the same in your scope pictures, should be since they are connected together.

[diegogeid]

My bad, i must've uploaded the wrong picture, both pin 2 and 3 look the same as the "pin 3" picture above. I think the problem relies on pin 6 which isn't changing according to the input of pin 5. I tried shorting pin 5 with pin 7 to force it to change, and for a while it does! Doing that changes the behaviour and starts to look normal, I see a waveform on pin 1 of u7 that changes as I swing a metal over the coil, but as soon as I adjust r14 it goes back to the old situation. I can make a video of that if you want. Any ideas? I'm getting more familiarized with the circuit, I'm going to try other things and keep you updated, I'm getting close! Thanks!

[green]

My bad, i must've uploaded the wrong picture, both pin 2 and 3 look the same as the "pin 3" picture above. I think the problem relies on pin 6 which isn't changing according to the input of pin 5. I tried shorting pin 5 with pin 7 to force it to change, and for a while it does! Doing that changes the behaviour and starts to look normal, I see a waveform on pin 1 of u7 that changes as I swing a metal over the coil, but as soon as I adjust r14 it goes back to the old situation. I can make a video of that if you want. Any ideas? I'm getting more familiarized with the circuit, I'm going to try other things and keep you updated, I'm getting close! Thanks!

Good your gaining, you will learn more if you try to solve it your self. If you can't ask and someone will suggest something.

[diegogeid]

Okay, it seems to work now, I played with r14 until I found a spot where it works, I can't get the timings indicated in the guide but all the waveforms seems fine, I'm assembling step 9 now, once I finish I'll ask you for tuning advice, thank you!

[diegogeid]

Hi guys, It's me again. I've finished the circuit and it seems to work, but the performance is so poor, I think it has to do with the sampler delay, here is the video detecting a pair of pliers, It detect's it at apporximately 3 cm: https://youtu.be/dj2eUcmOb6o
And here's what happens when I try to adjust r14 (I'm adjusting the delay pot back and forth with r14 near the place the problem starts). I'm reading on pin 6 of u4. The delay suggested on the guide says 40us, but here in the video the scope is displaying at 200 us per division and I can't reach the 40 uS because it "crashes" the system when I try to higher the speed: https://youtu.be/jveQxeJfHVg

[dbanner]

R14 is not the delay pot, it is trim 25k, the delay pot is 10k. Double check components around the 40106, make sure all is well. Check the voltage rails for correct supply. Try other 40106 chip. Remove gate legs of FET's, then scope pin 6 of U4 again.
One more thing, check for faulty pot.