Talking Skull Kit comments/recommendations

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dawgpile
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Talking Skull Kit comments/recommendations

Post by dawgpile » Fri Oct 10, 2008 9:47 am

After having successfully built the Talking Skull Kit, I wanted to share the following. (It's worth noting that I've contacted Carl @ Cowlacious and also Vern, the article's author)

These are in no particular order...

1. I found the directions for drilling the skull for the cable-tie jaw 'hinges' to be somewhat confusing. I went to Scary Terry's website and he has directions with photos that made it a lot clearer for me. In a nutshell, one of the holes you drill goes through the jaw and then through the skull, in one step. Then another hole is drilled near the back of the jaw. This is done for each side of the jaw.

2. Re: PCB assembly; The instructions neglect to mention installation of the coaxial power jack. This is minor as it's pretty obvious where it goes and it's the only part left over after following the instructions to the letter!

3. I made a design change to the servo control part of the circuit. Without going into a long diatribe here, suffice it to say I changed the value of R9 from 4.7K to 10K. The reason for this is to ensure that the servo is operated within its available range.

[You don't want to command the servo to a point which is beyond its physical capability as it causes the current drain to increase an order of magnitude to well over 500mA in addition to mechanical wear and tear. Using the 4.7K resistor produces a pulse-width of about 325uS and the servo's available range is only down to about 600uS. Changing the value to 10K produces a pulse-width of about 700uS, still within the servo's useable range. FYI, this happens when the Skull's jaw is commanded to open.]

4. In conjunction with item 3, I recommend the following procedure to properly adjust VR3, the jaw position when no signal is present(jaw closed position). (this assumes you've already built the control board and tested it)

After the piano wire is cut and bent according to the directions, go ahead and attach it to the servo horn and jaw. Remove the servo horn from the servo. Connect an audio signal to the board to cause the LVL LED to light and servo to rotate to its full CCW position. This represents the jaw full open so pick up the skull and open the jaw. Now attach the servo horn to the servo. The position of the horn should be somewhere between 6 o'clock(pointing straigt down) and 9 o'clock(pointing straight left facing the servo). Mine was about 7 o'clock.

Now, with the horn pushed on the servo(no need to put the screw in yet), remove the audio signal so the LVL LED goes out and the jaw closes. Adjust VR3 so the jaw 'just closes', but doesn't clench. The reason you don't want the jaw clenched is it really increases the current draw and if you're using batteries, there really is no need.

Apply an audio signal again and check that the servo travels back to full open. Cycle the servo back and forth to check your settings. When satisfied, don't forget to put the screw back in to hold the servo horn on the servo.

In my case, the servo only travels about 90 degrees to go from full open to full closed. All the while the current draw is less than 50mA.
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If anyone has any questions about what I did or why, I'd be happy to share more details. I hope you have as much fun with this as I have. :razz:

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VernGraner
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Re: Talking Skull Kit comments/recommendations

Post by VernGraner » Fri Oct 10, 2008 11:55 am

dawgpile wrote:After having successfully built the Talking Skull Kit, I wanted to share the following
Thanks for sharing! That's very useful info. :)

Vern
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Vern Graner

ccowley
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Re: Talking Skull Kit comments/recommendations

Post by ccowley » Tue Oct 14, 2008 10:58 pm

dawgpile wrote:Connect an audio signal to the board to cause the LVL LED to light and servo to rotate to its full CCW position. This represents the jaw full open so pick up the skull and open the jaw.

Another option to dawgpile's great comments and circuit changes = you don't have to apply audio to the circuit to get the servo to rotate to its full CCW positon, just adjust VR2 until the LVL LED lights up. You can rotate it back and forth to open and close the jaw for testing.

texevans
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Re: Talking Skull Kit comments/recommendations

Post by texevans » Mon Oct 19, 2009 4:43 pm

Clearly you guys have a pretty good handle on this project. Good tips.

I just finished assembly and got the whole thing built and almost working.

I've got power and the servo responds when I adjust the pots but it doesn't seem to be responding to the audio. The audio feed comes back out the output so I can verify that the signal is making it into the circuit.

Any idea where should I start troubleshooting?

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VernGraner
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Re: Talking Skull Kit comments/recommendations

Post by VernGraner » Wed Oct 21, 2009 11:33 am

texevans wrote:I've got power and the servo responds when I adjust the pots but it doesn't seem to be responding to the audio. The audio feed comes back out the output so I can verify that the signal is making it into the circuit. Any idea where should I start troubleshooting?
Hi! Sorry to hear you're having issues. As for troubleshooting, I would start by reviewing the "theory of operation" described in the original article on page 36:

The Talking Skull Kit - Sept 2008

The "How it Works, Theoretically Speaking" section goes into great detail as to how the circuit should work.

A few pointers to start with:
  • The presence of signal at J2 only means you have provided the signal in on J3 and that the parallel connections between J2 & J3 are corerctly soldered This doesn't mean the signal has been delivered to the rest of the circuit.
  • Check to make sure at least one of the jumpers J4 or J5 are engaged. These are used to control which channel of the audio signal is sent to the circuit. If you close both of them, the signal will be shorted to "mono".
  • Check to see if you are getting any audio signal at pin 2 of U2.1
If none of the above leads to a solution, please let me know and we can try some other steps. :smile:

Vern
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Vern Graner

texevans
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Re: Talking Skull Kit comments/recommendations

Post by texevans » Thu Oct 22, 2009 10:15 am

Thanks for the help.

I found the problem right away and it works great.

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