Need help on testing VCO.

Discuss x0x construction and related issues

Moderators: altitude, adafruit_support_bill, adafruit, phono, hamburgers

Please be positive and constructive with your questions and comments.
Locked
User avatar
k-rite
 
Posts: 65
Joined: Mon May 09, 2005 11:43 pm

Need help on testing VCO.

Post by k-rite »

Hi, I'm a little confused about how to test the VCO. The fabracation manual says to apply 2.0VDC to R89 and pin 5 of IC11. Do I put positive to R89 and negative to pin 5 of IC11? Which pin is pin 5 of IC11? Also it says to probe pins 1 or 3 of the waveform switch. Where do I connect the leads of my headphones on the switch? Which pins are what? Can someone help me out?

Tom

User avatar
k-rite
 
Posts: 65
Joined: Mon May 09, 2005 11:43 pm

Post by k-rite »

O.K., so I am able to hear sound when touching the switch contacts (sounds like a helicopter). When I touch the second most northern contact I hear sound, but when I flip the switch it stays there. However if I touch the third most northern contact I get sound when the switch is one way, but not the other. I would think the second most northern contact should also only make sound when the switch is one position and not the other. Is there something wrong with my switch or is this normal? I also still need to know where to hook my power supply with the 2VDC. I don't want to damage anything by hooking it up incorrectly. Anybody got some advice?

User avatar
subatomic
 
Posts: 523
Joined: Wed May 11, 2005 3:12 pm

Post by subatomic »

when probing, I ground the headphone sleeve part to the pin2 of the jumper that comes off the psu. right next to it is a resistor that is also connected to pin2. I just tap off that resistor, it's easy.

Then with the aligator on the sleeve of the stereo jack, I touch the tip of the jack to the top or the bottom pin of the SAW/SQR switch (just ignore the ring part of the jack). The middle pin I think is the output, so depending on what is switched it should have that waveform... If I'm wrong about which pin is what, it's no big deal, you'll hear it by probing. I think the fab manual may say for certain...

The sqr wave might sound like a sin wave, or be faint. If you dont have the ref voltage hookup up (2.0V) to set the pitch of the VCO, then the voltage might be floating around a bit causing the pitch to be high, low, all over...

User avatar
k-rite
 
Posts: 65
Joined: Mon May 09, 2005 11:43 pm

Post by k-rite »

So, when the switch is in one position should I hear a waveform on just one pin or both pins, because when the switch is the down position I can hear sound on the second from the top pin only. When the switch is in the up position I can hear a waveform on the second from the top pin and the pin below it. Is this correct or is my switch bad?

Also where do I hookup my power supply (2VDC) leads? Does the positive go to R89 and the negative to R179 of the PSU?

User avatar
k-rite
 
Posts: 65
Joined: Mon May 09, 2005 11:43 pm

Post by k-rite »

I figured out where to hook all the leads for testing now, but I'm still not sure about the switch behavior (see above post). I'm going to try and tune it tommorrow with a software oscilloscope. Wish me luck.

Jonnay
 
Posts: 142
Joined: Thu Jun 02, 2005 12:28 pm

Post by Jonnay »

The top pin should be the saw wave.

The bottom pin should be the square wave.

The middle pin will be whatever is currently switched and will always have a waveform.

User avatar
subatomic
 
Posts: 523
Joined: Wed May 11, 2005 3:12 pm

Post by subatomic »

k-rite wrote:Also where do I hookup my power supply (2VDC) leads? Does the positive go to R89 and the negative to R179 of the PSU?
Whenever they say "hook up a voltage to here"... that means...
1.) hook the neg (black) of your bench power supply to the same ground as the x0x (i.e. pin2 of the jumper wires that come from the PSU to the mainboard - or anything connected to that, the resistor next to it, ground rails, etc...).
2.) hook the pos (red) of your bench power supply to wherever they're telling you.


If you don't have the same ground between both power supplies, then how would you define the voltage of the positive of one relative to the ground of the other? You can't, it's not really definable, at worst it could be hugely different, at best it might be close or not enough, possibly it's floating around wildly. In any case you can't really know unless you make all grounds the same, then you know what voltage you're applying. remember voltage is a relative thing. it's the potential difference between two points. when bringing two PSU's together you have to bring them into the same relative space. sort of a syncronization.

User avatar
k-rite
 
Posts: 65
Joined: Mon May 09, 2005 11:43 pm

Post by k-rite »

Jonnay wrote:The top pin should be the saw wave.

The bottom pin should be the square wave.

The middle pin will be whatever is currently switched and will always have a waveform.
Well then I got problems. Pin 1 (top) always produces a waveform. Pin 2 (middle) only produces waveform when switch is in the saw (down) position. Pin 3 (bottom) produces no waveform at all. Can someone verify that this is not normal behavior? Does anyone have some suggestions?
subatomic wrote:Whenever they say "hook up a voltage to here"... that means...
1.) hook the neg (black) of your bench power supply to the same ground as the x0x (i.e. pin2 of the jumper wires that come from the PSU to the mainboard - or anything connected to that, the resistor next to it, ground rails, etc...).
2.) hook the pos (red) of your bench power supply to wherever they're telling you.
I see, thank you for clarifying for me.

User avatar
k-rite
 
Posts: 65
Joined: Mon May 09, 2005 11:43 pm

Post by k-rite »

After digging some more I now understand that the triangle waveform comes from Q8 into the switch on pin 3. So if pin 3 isn't making any sound I should see if Q8 does. I'm going to check it out when get home today. I'm also going to check Q28 for the square waveform. If both of these are producing a waveform, then I guess my switch is bad. Please correct me if I'm wrong in this thinking.

User avatar
subatomic
 
Posts: 523
Joined: Wed May 11, 2005 3:12 pm

Post by subatomic »

Don't worry. The SQR comes through on most headphones as either a very quiet sin wave, or you won't hear it at all depending on the headphones. Remember they said use cheap. But that's not very specific. Your "cheap" might actually have qualities that make the sound faint or too quiet.

What you're describing is normal. Just continue building... :)

User avatar
k-rite
 
Posts: 65
Joined: Mon May 09, 2005 11:43 pm

Post by k-rite »

subatomic wrote:Don't worry. The SQR comes through on most headphones as either a very quiet sin wave, or you won't hear it at all depending on the headphones. Remember they said use cheap. But that's not very specific. Your "cheap" might actually have qualities that make the sound faint or too quiet.

What you're describing is normal. Just continue building... :)
O.K., it's all making sense now. I would have thought since I can hear the square wave that I would also be able to hear the triangle, but since I can't thats why no sound is coming out of pin 3 and only sound is coming out pin 2 when the switch is one postion and not the other. I'm going to try some other headphones and see what I get. I'm also going to try one of those free software oscilloscopes too. Thanks man!

User avatar
subatomic
 
Posts: 523
Joined: Wed May 11, 2005 3:12 pm

Post by subatomic »

I think it should be the saw wave that you hear, and the sqr is quieter. more harmonics (and energy) in the saw...

use an oscilloscope, you'll see it...

Locked
Please be positive and constructive with your questions and comments.

Return to “Making x0x”