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Interactive Snowman Project
Moderators: AmyCowen, kgudger, bfinio, MadelineB, Moderators
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deleted-342262
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Interactive Snowman Project
Unable to make this work. We have rebuilt the board a few times, have bought new components and can't imagine why it won't move. We've tested individual components for continuity. Project is due on 2/12 and we've hit this roadblock. Got the snowman molded in clay and covered waiting to install the servo motor, etc. Please offer any help at this point.
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Re: Interactive Snowman Project
Hi jhupp99-
You've apparently managed to stump the experts. I hope you figured out the problem and fixed it yourself. If you had asked something in chemistry, biology or other basic sciences... You did say that you rewired it several times and that was smart to try. It is easy to miss a wire here or there and if you look back at other questions here, you'll see that 'check the wiring' is a standard response to questions like this. You've done that and more so something else must have been wrong.
You said the servo didn't move but you didn't say whether it was being held in position or whether you could move it by hand. That makes a huge difference. A servo requires a continuous pulse train to hold a position. If (a) the timer chip isn't outputting anything, the servo will 'let go' and be movable by hand. If (b) it's holding steady then the timer is sending out pulses. If (b) is true, then the problem is the photo cells. If (a) is true, then your problem is elsewhere. You also said that you checked the continuity of components. I know that other users and experts on this forum have suggested that, but you can really only check continuity on wiring. Components *can* be tested with some method that's appropriate for that component- for example, you can measure the resistance of a resistor with a multimeter, or measure a diode with the resistance function of a meter and see that it conducts one way and not the other. Things like capacitors can't be tested so easily.
So what went wrong with your circuit? Well, if the servo was holding steady but wouldn't move, I'd check the wiring around the light sensors. The two of them work together to function as a voltage divider. The battery supply puts 6 volts across the pair of them. If both resistors are getting the same amount of light, the voltage in the kiddie would read about 3 volts. You can see them work on your mutimeter by setting it to Volts, probing the connection between the two photocells and shielding one and then the other from the room light. You'll see the voltage go up and down as you block the light.
If the servo is easily moved by hand, you simply aren't getting any pulses out of the timer. Or perhaps you are, but they're really wrong. Did you use the correct values of resistors? Sometimes it's hard to read the colors on the tiny bands. Is the diode in place and not backwards? If you put that in backwards the timer won't work. The right tool for debugging the timer is an oscilloscope but many people don't have one. If you had one, you could watch the capacitors to see if they're charging and discharging as they should, and look at the output to see if you're getting pulses out from pin 3 of the timer. Here's a trick you can try to look for pulses without having an oscilloscope - an LED connected to a 6V battery through a 330 ohm resistor would light up. If you connected to a pulse train instead (like the one you're trying to create here), it will light up dimmer in relationship to the duty cycle of the pulses. Wider pulses will appear brighter than narrow ones. An easy test then is to take an LED and a 330 ohm resistor in series and connect them between across the battery. See how bright it is. Then connect that setup between pin 3 of the chip and ground. If it's just as bright or completely off, you're not getting pulses. If it's dimmer, you are. And finally, if the LED test shows a dim LED but the servo isn't holding position, you may have another component that's the wrong value and the servo simply can't understand it.
Howard
You've apparently managed to stump the experts. I hope you figured out the problem and fixed it yourself. If you had asked something in chemistry, biology or other basic sciences... You did say that you rewired it several times and that was smart to try. It is easy to miss a wire here or there and if you look back at other questions here, you'll see that 'check the wiring' is a standard response to questions like this. You've done that and more so something else must have been wrong.
You said the servo didn't move but you didn't say whether it was being held in position or whether you could move it by hand. That makes a huge difference. A servo requires a continuous pulse train to hold a position. If (a) the timer chip isn't outputting anything, the servo will 'let go' and be movable by hand. If (b) it's holding steady then the timer is sending out pulses. If (b) is true, then the problem is the photo cells. If (a) is true, then your problem is elsewhere. You also said that you checked the continuity of components. I know that other users and experts on this forum have suggested that, but you can really only check continuity on wiring. Components *can* be tested with some method that's appropriate for that component- for example, you can measure the resistance of a resistor with a multimeter, or measure a diode with the resistance function of a meter and see that it conducts one way and not the other. Things like capacitors can't be tested so easily.
So what went wrong with your circuit? Well, if the servo was holding steady but wouldn't move, I'd check the wiring around the light sensors. The two of them work together to function as a voltage divider. The battery supply puts 6 volts across the pair of them. If both resistors are getting the same amount of light, the voltage in the kiddie would read about 3 volts. You can see them work on your mutimeter by setting it to Volts, probing the connection between the two photocells and shielding one and then the other from the room light. You'll see the voltage go up and down as you block the light.
If the servo is easily moved by hand, you simply aren't getting any pulses out of the timer. Or perhaps you are, but they're really wrong. Did you use the correct values of resistors? Sometimes it's hard to read the colors on the tiny bands. Is the diode in place and not backwards? If you put that in backwards the timer won't work. The right tool for debugging the timer is an oscilloscope but many people don't have one. If you had one, you could watch the capacitors to see if they're charging and discharging as they should, and look at the output to see if you're getting pulses out from pin 3 of the timer. Here's a trick you can try to look for pulses without having an oscilloscope - an LED connected to a 6V battery through a 330 ohm resistor would light up. If you connected to a pulse train instead (like the one you're trying to create here), it will light up dimmer in relationship to the duty cycle of the pulses. Wider pulses will appear brighter than narrow ones. An easy test then is to take an LED and a 330 ohm resistor in series and connect them between across the battery. See how bright it is. Then connect that setup between pin 3 of the chip and ground. If it's just as bright or completely off, you're not getting pulses. If it's dimmer, you are. And finally, if the LED test shows a dim LED but the servo isn't holding position, you may have another component that's the wrong value and the servo simply can't understand it.
Howard