Small NPN 3904 relay style circuit

In summary, the transistor in the first circuit is not triggering the coin meter, and the transistor in the second circuit is not supplying enough voltage to the coin meter. The problem may be due to a lack of voltage being supplied to the devices, or a mistake in the circuit.
  • #1
Nevian
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I am currently trying to make a small circuit work, and more than just trying different things until it does work, I wanted to hopefully get an explanation to why it is not working. I am a novice, I only started dabbling in my free time recently and thought I had a decent if only vague understanding of how a NPN3904 Transistor would work. I have two separate circuits. One is a 5 volt circuit with a button on it, the second is a 6volt circuit with a coin meter on it. The button triggers a keyboard press that will eventually trigger that a coin dropped through my coin door, at this time I would like the NPN3904 turn on and flip the coin meter. For whatever reason, when I measure voltage at the emitter of the transistor there only seems to be 1 volt passing through and there for not enough to trigger the coin meter. I am using a 1k ohm resistor on the base of the transistor. What am I missing?

I am attaching a crude drawing, please explain what I am missing or how I can design this so it will work?

http://i1370.photobucket.com/albums/ag263/nevian2/RANDOM/npn_zpsf9e63613.png~original
 
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  • #2
Firstly, welcome to PF. Now the questions;

Is the coin meter a two terminal device? Does it use a relay solenoid driving a mechanical counter?
Or is it a three terminal electronic counter?
 
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  • #3
It's a mechanical coin meter with only two leads. Once 6v is supplied it clicks over and will only do so again once power is removed and reapplied.
 
  • #4
Nevian said:
It's a mechanical coin meter with only two leads. ...

doesn't tell us a lot

is it a relay/solenoid ?
at the moment ... where are your 5V and 6V rails being supplied from ?
does the 5V side really need to be 5V or can it also be 6V ?

also a big part of the problem is you haven't shown complete power supplies
I will redraw the circuit for you

Dave
 
  • #5
OK a pair of circuits one for all 6V supply and one for 5V and 6V supplies
take your pick

Till you respond, I will assume the coin thing is a relay/solenoid type of thing and is denoted by the coil and the relay switch in my diagram
as such, because it's an inductive load, you will need the 1N4007 (or similar) diode across the coil as shown

RelaySw1.GIF


The base resistor value isn't too critical somewhere around 2k2 - 5k6 will be fine

cheers
Dave
 
  • #6
I am not certain this is the coin meter I have, as I am not at home, I am at work, but it is similar to this.
http://www.twistedquarter.com/index...ducts_id=848&zenid=j84hbcueaagphq8kvdlaglljt4

Sorry about the late response, I work nights on the Pacific Coast. Thanks for the help.

As for either ckt being supplied from the 6v, I have two separate power sources and I would like to keep them that way, I do not want to accidentally fry the iPac that I am using in my MAME.
 
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1. What is a Small NPN 3904 relay style circuit?

A Small NPN 3904 relay style circuit is a type of electronic circuit that uses a small NPN 3904 transistor as a switch to control the flow of current through a relay. The circuit is commonly used in electronic devices to control the operation of various components.

2. How does a Small NPN 3904 relay style circuit work?

The circuit works by using the NPN 3904 transistor as a switch. When a small current is applied to the base of the transistor, it allows a larger current to flow from the collector to the emitter, which in turn activates the relay. When the current to the base is removed, the transistor turns off and the relay is deactivated.

3. What are the advantages of using a Small NPN 3904 relay style circuit?

One advantage of this circuit is its small size, making it suitable for use in compact electronic devices. It also has a low power consumption and can handle relatively high currents, making it versatile for various applications.

4. What are the common uses of a Small NPN 3904 relay style circuit?

This type of circuit is commonly used in electronic devices to control the operation of motors, lights, and other components. It can also be used in automation systems, power supplies, and other applications that require a simple and compact switching mechanism.

5. How can I build a Small NPN 3904 relay style circuit?

To build this circuit, you will need a NPN 3904 transistor, a relay, a power source, and other necessary components such as resistors and capacitors. You can find step-by-step instructions and diagrams online or in electronics textbooks. It is important to follow safety precautions and double-check your circuit before powering it on.

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