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Step 2The 555 timer circuit
I always just hoped that, that I'd meet some nice friendly girl, like the look of her, hope the look of me didn't make her physically sick, then pop the question and... um... settle down and be happy. It worked for my parents. Well, apart from the divorce and all that! - Four Weddings and a Funeral
OK, we have our mechanical part. Now we need something to drive it. The 555 is a really nice little workhorse of a chip. We are going to use it to create the pulses that will simulate a heart beat.
The 555 is designed to put out a timed pulse depending on the values of the resistors and capacitor attached to it. I played around a little and eventually decided on a 47uf capacitor, and two 3.3k resistors. This gives a nice beat, slightly faster than a normal human heart.
The diagram below explains how to lay it out. I had to use the 3906 transistor on the output, as the pulse from the chip is just not strong enough.
If the diagram below is Greek to you, I would encourage you to check out these sites. They have some fantastic information to get you started:
http://www.kpsec.freeuk.com/breadb.htm
http://home.cogeco.ca/~rpaisley4/LM555.html
You can see that once you have it together, it looks easier than it appears. These are the basic steps I use:
1. Connect Pins 4 and 8. If you are free forming this, you can bend the pins under the body.
2. Connect pins 6 and 2. I usualy run a jumper over the top of the chip to avoid bending the legs off.
3. Solder the capacitor across pins 1 and 2, with the negative side on pin 1.
4. Solder one of the 3.3k resistors across pins 7 and 8
5. Solder the other 3.3k resistor across pins 6 and 7.
6. solder the negative power lead to pin 1
7. solder the positive lead to pin 8.
I would apply power at this point and check to make sure I am getting a pulse by putting an LED across pins 3 and 1, with the positive lead on pin 3. If the chip heats up at all, something is connected wrong. If you have a nice pulse, then: (with the 3906 in "dead bug" mode, flat side up, pins facing you)
8. solder the middle leg of the 3906 to pin 3.
9. Solder the left leg to ground (pin 1)
Now, you need to connect the "eye" to the circuit. There will be 4-6 connections on the eye. take a battery or power supply and test the contacts to see which ones make the coil jump up. some contacts will make is slide to the side, some up, some down. you will get the idea. When you have the right ones...
10. solder the right leg to one of the connections on the coil from the CD Rom drive
11. Solder a connection from the other connection on the coil to the + source (pin 8 or 4)
I find it's not generally needed to solder pin 5 of the 555 to anything. it just works.
Now, when you connect the power, you should see the "eye" jump up and down. If not, check your connections. The biggest mistake I usually make is connecting the 3906 backwards.
OK, we have our mechanical part. Now we need something to drive it. The 555 is a really nice little workhorse of a chip. We are going to use it to create the pulses that will simulate a heart beat.
The 555 is designed to put out a timed pulse depending on the values of the resistors and capacitor attached to it. I played around a little and eventually decided on a 47uf capacitor, and two 3.3k resistors. This gives a nice beat, slightly faster than a normal human heart.
The diagram below explains how to lay it out. I had to use the 3906 transistor on the output, as the pulse from the chip is just not strong enough.
If the diagram below is Greek to you, I would encourage you to check out these sites. They have some fantastic information to get you started:
http://www.kpsec.freeuk.com/breadb.htm
http://home.cogeco.ca/~rpaisley4/LM555.html
You can see that once you have it together, it looks easier than it appears. These are the basic steps I use:
1. Connect Pins 4 and 8. If you are free forming this, you can bend the pins under the body.
2. Connect pins 6 and 2. I usualy run a jumper over the top of the chip to avoid bending the legs off.
3. Solder the capacitor across pins 1 and 2, with the negative side on pin 1.
4. Solder one of the 3.3k resistors across pins 7 and 8
5. Solder the other 3.3k resistor across pins 6 and 7.
6. solder the negative power lead to pin 1
7. solder the positive lead to pin 8.
I would apply power at this point and check to make sure I am getting a pulse by putting an LED across pins 3 and 1, with the positive lead on pin 3. If the chip heats up at all, something is connected wrong. If you have a nice pulse, then: (with the 3906 in "dead bug" mode, flat side up, pins facing you)
8. solder the middle leg of the 3906 to pin 3.
9. Solder the left leg to ground (pin 1)
Now, you need to connect the "eye" to the circuit. There will be 4-6 connections on the eye. take a battery or power supply and test the contacts to see which ones make the coil jump up. some contacts will make is slide to the side, some up, some down. you will get the idea. When you have the right ones...
10. solder the right leg to one of the connections on the coil from the CD Rom drive
11. Solder a connection from the other connection on the coil to the + source (pin 8 or 4)
I find it's not generally needed to solder pin 5 of the 555 to anything. it just works.
Now, when you connect the power, you should see the "eye" jump up and down. If not, check your connections. The biggest mistake I usually make is connecting the 3906 backwards.
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In your schmatic and instructions you state using a 3906 transistor.
your smybol for a 3906 transistor is wrong.A 3906 is a PNP transistor.
you have a smybol for a NPN transistor which is a 3904 transistor.
which transistor are you using a npn 3904 or a pnp 3906 transistor.
the circuit may need a resistor on the base of the transistor to lower
the base current.