Visible electric current circuit

[tumblingtwister]

I'm planning to build a variant of this circuit as a mini project for my design class.
http://amasci.com/viselect/schem1.gif

I need help analyzing it. Firstly, I haven't quite understood the operation of the precision full wave rectifier in the circuit. When I simulate it on Multisim, I don't get a full wave rectified output across the diodes. Is it a full wave rectifier? This is the designer's explanation of the circuit
VISIBLE ELECTRIC CURRENT

Secondly, what is the function of the transistor 2N3904 in the circuit? Thirdly, it's output goes to a series of NAND gates, whose function I am unable to figure out.

I will greatly appreciate any help you guys can provide me.
Thanks.

 

[ccurtis]

The 2n3904 transistor converts the varying output voltage of the op amp to a two state logic level signal suitable for input to the NAND gates. The switching point between logic levels is determined by the combined settings of the DIR CAL, DEAD BAND, and GAIN pots and the circuit input level.

The pair of NAND gates immediately to the left of the 194 shift register control the mode of the shift register (either shift left, shift right, load, or do nothing). The single NAND gate to the left of that pair ensures that one of the inputs to each NAND in the pair is always of opposite logic state so that the shift register will shift right or shift left depending on the logic state at the output of the transistor. The outside inputs to the pair of NAND gates are connected to the appropriate outputs of the shift register to generate the desired shifted pattern of LEDS.

The precision full-wave recifier is a valid textbook design, except I don't know why two diodes are used in series in each leg, instead of the usual single diode in each leg. Perhaps you are not simulating the entire circuit which is composed of the two op amps on either side of the diodes, the diodes, all of the 220k resistors, the voltage from the dead-band control, the voltage from the zero control, and the voltage from the left-most op amp.

 

[tumblingtwister]

Thanks a lot for the explanation. That made a lot of sense. One more question about the NAND gate connected to pin 9 of the 194. What does the positive sign above it indicate? I've never seen that before. On a similar line, the NAND gate connected to pin 11 of the 194 has a ground.
By the way, the simulation of the full wave rectifier now works. I hadn't connected the transistor in the circuit. As soon as I connect it, I get a full wave output across the two points fed to the next op amp. Any idea why that happens?

 

[KMoffett]

One more question about the NAND gate connected to pin 9 of the 194. What does the positive sign above it indicate? I've never seen that before. On a similar line, the NAND gate connected to pin 11 of the 194 has a ground.

Those are the power connections on the 74LS00's chip. Pin 14 is (+) and pin 7 is (-).

Ken

 

[ccurtis]

By the way, the simulation of the full wave rectifier now works. I hadn't connected the transistor in the circuit. As soon as I connect it, I get a full wave output across the two points fed to the next op amp. Any idea why that happens?

The only thing I can think of is that by adding the transistor you included a ground node in your simulation which is necessary to have at least one of in any simulation. The transistor and the resistors connected to it are not part of the rectifier circuit at all.

 

[ccurtis]

Looking at the schematic, I notice an error based soley on the inventor's description. The wire connected to pin 3 of the LM331 should, instead, be connected to the collector of the transistor. And the wire connected to the collector of the transistor should, instead, be connected to pin 3 of the LM331.

 

[duffy]

I think this is a great idea. Have you considered using chasing rope lights for the cables?
**broken link removed**

It would look more like wires than that cylinder.

 

[tumblingtwister]

Looking at the schematic, I notice an error based soley on the inventor's description. The wire connected to pin 3 of the LM331 should, instead, be connected to the collector of the transistor. And the wire connected to the collector of the transistor should, instead, be connected to pin 3 of the LM331.

So in effect, the collector of the transistor would be connected to the NAND gates, so that it would control the direction of shift of the 194? Is that right?

What then would be the function of the 7493 counter?

I really appreciate the help, thanks a ton.

 

[tumblingtwister]

I think this is a great idea. Have you considered using chasing rope lights for the cables?
Chasing Rope Lights, custom chasing rope lights, and rope light accessories

It would look more like wires than that cylinder.

That's a brilliant idea! I'll order one of them right away. Would you happen to know what the voltage and current constraints for those lights might be? You see, I'm in India, and I'll be ordering the lights from the US. I just want to make sure that I don't blow them up just before I have to demonstrate my project! Thanks for the suggestion!

 

[duffy]

No, I don't know anything about them, I just saw them on some houses at Christmas.

 

[ccurtis]

So in effect, the collector of the transistor would be connected to the NAND gates, so that it would control the direction of shift of the 194? Is that right?

Yes, that is correct.

What then would be the function of the 7493 counter?

That counter is dividing the output frequency of the LM331 by 2, 4, 8, or 16 depending on if the NAND gate following it is connected to the Q0, Q1, Q2, or Q3 output of the counter, respectively (the schematic doesn't show which Q output). The 4.7K resistor, .001 uf capacitor, and diode output a short pulse to the NAND gate on the falling edge of the Q output of the counter. I presume this is because the inventor wanted a complete clock pulse (rising and falling edges) for the 194 counter at that time to allow the mode control of the shift register to take effect without waiting for the usual next edge at the Q output. This might be important if the frequency is very low, and thus the wait for the next transition very long.

 

[jwb123]

In this case I would use some chasing rope light as well. I found this website that even sells led chasing rope light **broken link removed**