Rev D Build #2 Started

[geoscash1]

Ok, figured I would get back to this little project and started a new build (1st one didn't go well for whatever reason).

I will log each step as I go here so to keep a nice record of where it is at in the process. I am still learning how to use my scope (rookie)
so may not have things set properly by comparison to others on here.

(I am currently up to step 4 and forgot to take pics of first 2 steps so added pics after parts installed)

I do need some help with scope settings so I know that I am looking at the right thing or having it look as it should correctly. It would be great to have some screen shots of scope settings for each step with a visual of what each step should look like, sort of like the mirage build doc so some of us rookies wouldn't have to ask dumb questions...

So lets get this party started...


Step 1, installed components - tested with meter = -4.99v

[geoscash1]

Step 2 - +5v

Step 2, installed components- tested with meter = +4.98v

[geoscash1]

Step 3 - tx oscillator

Step 3, installed components - tested tx oscillator with scope - 57us
(scope settings - 2v div/10us time div)

[geoscash1]

Step 4 - TX circuit

Step 4, transmit circuit components installed, measured flyback with scope but am not exactly sure how to read what I am seeing. The scope settings are
channel 1 - 2v div/10us time div, probe set to x10, attached across damping resistor R1 - coil attached is 329uH.

Tried the headphone test and can hear a nice clear high pitched tone in the speaker.






I will wait to move on to step 5 after confirming step 4 is good or needs to be changed.

[kt315]

if you use a probe-devider 1:10 then you have 20V div. then flyback P-to-P is 120V, anotherway you have 12V that is strange.

[geoscash1]

Hi kt315,

The difference between the 2 flyback photos, is one of them I tried 20us time delay setting to see what it looked like. Both photos the scope is set to 2v/div with probe at
x10.

[kt315]

ok. it was not clear that you use probe 1:10. enough then to write 'is set to 20V/div'.

[Chet]

Step 4, transmit circuit components installed, measured flyback with scope but am not exactly sure how to read what I am seeing. The scope settings are
channel 1 - 2v div/10us time div, probe set to x10, attached across damping resistor R1 - coil attached is 329uH.

Tried the headphone test and can hear a nice clear high pitched tone in the speaker.


[ATTACH]34169[/ATTACH]
[ATTACH]34170[/ATTACH]
[ATTACH]34171[/ATTACH]

I will wait to move on to step 5 after confirming step 4 is good or needs to be changed.

Hi geoscash1

It appears in the photo that your Cal knob may not be fully clockwise?

Attached are some scope shots for comparison.

Have a good day,
Chet

[geoscash1]

Thanks chet

You are correct, I did forget to turn it back off (the cal knob) but it made no difference in the on screen image. I was messing around changing settings to see how it changed what I was seeing using different time divs and voltage divs.

Thanks for the beautifully clear scope screen shots. Based on yours, it looks like mine is on the right path, just need to figure out why it is only 120v instead of the "350v" that is stated in the build doc. May be mostly the scope operator (me...lol), still learning how to use one whilst building these projects but am enjoying how it shows you what it going on behind the curtains so to speak.

[kt315]

do you use irf510? Vdss minimal 100V is according datasheet.

[geoscash1]

kt315, I used an IRF740, its what was called for in the build doc.

[geoscash1]

Changed scope setting and cleaned bottom of board

Ok, I cleaned the bottom of the board just to make sure there were no shorts from solder flux then I changed the settings on my scope so it is set at 5v/div 50us/time div and am now getting this on the scope.

If I understand this correctly, it shows 7 divisions of 50 us which would be multiplied by 10 (x10 probe) which would be the correct reading of 350v or am I wrong in my thinking?

[Chet]

Ok, I cleaned the bottom of the board just to make sure there were no shorts from solder flux then I changed the settings on my scope so it is set at 5v/div 50us/time div and am now getting this on the scope.

If I understand this correctly, it shows 7 divisions of 50 us which would be multiplied by 10 (x10 probe) which would be the correct reading of 350v or am I wrong in my thinking?

[ATTACH]34177[/ATTACH]

Hi geoscash1

Seven vertical divisions of 50 volts equals 350 volts which is good. This voltage will vary with with different coils and damping resistor values.

The Horizontal sweep speed is set at 50us per division. Your screen indicates approximately 6.5 horizontal divisions from pulse to pulse. Pulse frequency is 1 divided by 6.5 times 50us equals 1 divided by 0.000325 equals 3,077 Hz per second. The right hand settings on your scope aren't visible. If there is a variable Horizontal control it needs to be reset. The pulse frequency should be approximately 1000 Hz which is equal to 1000us between pulses.

If the scope settings are ok then check the resistor and capacitor values around the 555 oscillator circuit.

Have a good day,
Chet

[geoscash1]

Recheck scope settings

Hey Chet,

Thank you for that info, you were correct, I had my var horizontal sweep on so I turned it off and rechecked. Had to adjust the trigger. I triple checked the values (R8/R9/C6) and they are correct.

Based on what I am understanding now, the screen has 10 divs of 50 us sweep (500us per full screen) and using the position knob I can scroll the screen to the right another 10 before seeing the pulse again so it is close to 1000us. I'll play with the scope settings some more so I can learn more how to see what were looking for. This scope isn't the best but I am understanding the screen divisions and how they relate to this so hope to get this down better through this build.

So took a new pic of the scope shot.


Thanks again for all of your help and you as well have a super day,
Geo

[Chet]

Hi Geo

Sounds good. If you set the horizontal sweep speed to 0.2 ms/division = 200us/div you should see two pulses separated by approximately 5 divisions.

Your scope is quite good for this work. It has a 20 MHz input bandwidth which is very good for any metal detector circuity that you will need to observe.

Have a good day,
Chet