Introduction: Switching Circuit

Picture of Switching Circuit

In this Instructable (my first) I have posted the circuit design that I am currently fiddling with for its eventual use in my coilgun. When it is finished it will serve as the activation switch for a second coil. Like I said; I am still modifying the circuit and I'm currently looking for a bit of advice, so any ideas would be helpful.

Continue on to the next page for a few more details.

Step 1: The Parts

Of course with any electronics project you have to have a parts list. Here it is so far.

3904NPN Transistor
3906PNP Transistor
Diode (not needed)
LDR (Highest Ohm rating I could find @ radioshack)
3-16V Buzzer

The buzzer is on the circuit in place of the relay that will eventually be used to short out my capacitor bank.

Step 2: Schematic

Picture of Schematic

The idea of my circuit consists of an LED, LDR, relay, and a digital switch. when put togeather the LED and LDR will be placed on opposite sides of my coilguns barrel and the digital switch will turn ON and stay on when the projectile passes between the light and the light detector. My current problem (current...lol) is that the switch does just the opposite. When the light is introduced, the circuit is turned OFF and stays off.

Step 3:

Basically what this Instructable is an attempt to do is create an SCR without having to buy one through some online electronics superstore. I'm so close, but I'm definitely stumped at this point. If I have left out any info that would help you help me, feel free to message me. Ill be back with an answer ASAP.

Comments

randofo (author)2009-01-26

This project looks awesome but there isn't enough documentation of you actually making it to be a full Instructable. There are two things which you could do. 1) If you happen to have images of you making your project you can create some more steps, add those additional photos into your Instructable and then republish your Instructable. 2) If you don't have any more pictures of you working on your project, that's ok too. That just means that your project is better suited to be submitted as a slideshow. Your images are already in your library, and you can use the same text that you have already written for your Instructable so it should only take a few minutes to create your slideshow and show the world what you made! Thanks for your submission and let me know if you have any questions along the way.

admin (author)2009-01-21

This project looks awesome but there isn't enough documentation of you actually making it to be a full Instructable. There are two things which you could do. 1) If you happen to have images of you making your project you can create some more steps, add those additional photos into your Instructable and then republish your Instructable. 2) If you don't have any more pictures of you working on your project, that's ok too. That just means that your project is better suited to be submitted as a slideshow. Your images are already in your library, and you can use the same text that you have already written for your Instructable so it should only take a few minutes to create your slideshow and show the world what you made! Thanks for your submission and let me know if you have any questions along the way.

theblindferrengi (author)2009-10-14

cany tou just wire the relay in so the turning off [of the relaycoil] will close the circut,

Questioneverything13 (author)2009-07-04

Forget about using an LDR they are to slow use a photo transistor.

d-lite (author)2009-03-30

The first thing you should do is learn about photo-transistors. The LDR is totally unsuitable for anything that requires precision, and, a rail gun needs milli-second timing at the very least! For the same reason, forget about SCRs - use MOSFETs instead!

Wesley666 (author)d-lite2009-04-12

He's right. Probably a better choice would be IR transmitter and receiver or laser and a different LDR. The problem with the circuit is that it turns ON when it should not and OFF when it should not if I am correct. To correct this, first, is voltage in + or -. Then what you need to do is have the amplifying transistor, PNP, base connected to LDR output, collector to - (NEGATIVE) ground and the emitter to the base of the NPN transistor. Connect the emitter (EMITTER!) to - (NEGATIVE) Ground and the collector to buzzer or relay. Of course make sure the buzzer/relay output is connected to + (POSITIVE) and the LDR input to - (NEGATIVE) Ground. This should work but it is hard to think about, easier if it is written down. When actually using this for the coil or rail gun, definitely go for MOSFET (Check to make sure they will work BEFORE buying/E mail company to get info) and definitely use either a more precise LDR and Laser or IR Transmitter and Detector. Hope this helps.

sabre (author)Wesley6662009-06-15

Wow. Thanks for the input. Thats what I was looking for when I posted this.

MacDynamo (author)2009-06-11

I probably sound noobish to most hobbyists, but for my own and other viewers benefits, what's an LDR? The schematic almost makes it look like a photosensitive cell for detecting light and dark.

Muscelz (author)2009-03-05

and what the buzzer for?

Wesley666 (author)Muscelz2009-04-12

Relay

Muscelz (author)2009-03-05

aye mate, that aint a coil gun circuit. delete the Instructable ur making urself look stupid lol. buy urself a SCR, they're pretty cheap, and stop trying to reinvent them, because no NPN or PNP setup would be able to cope with hundreds of amps

Wesley666 (author)Muscelz2009-04-12

Also I doubt he is using hundreds of amps to power this. He is probably using just a nine volt battery to power external circuits for the gun.

Wesley666 (author)Muscelz2009-04-12

you can get transistors that will, but they are mighty expensive. I have some that handle 100 amps at 600 volts, but they are also beasts.

sabre (author)Muscelz2009-03-07

your definitely right. its not the main circuit for my coilgun, but it is a piece of circuitry that I was planning on using for my coilgun. Also I don't intend this setup to conduct the amount of voltage that would be put through my coil. This circuit simply opens/closes a relay represented by the buzzer. Its been a while since I have actually worked on this design. The only reason I have left it up is to see what other people think about the concept.

Muscelz (author)sabre2009-03-09

oh! well ur reason is understandable, soz about sayin dat b4 :), kool as

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Bio: Student @ University of North Texas working towards a Mechanical and Energy Engineering Major. I do all kinds of fun little projects. I'm currently trying ... More »
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