dc motor control question

[mvagusta]

cdrom tray dc motor + voltage

Hi everyone

Does anyone know of a dc motor control circuit, that makes a dc motor perform in the same way as a cdrom tray motor. I've been searching but haven't found anything yet?

So in other words, you hit a button, the motor drives until the limit switch is triggered and then the motor stops. If you hit the same button again, the motor drives in reverse, until the home posistion switch is triggered.

Thanks for reading

 

[Prototyp_V1.0]

ttl dc motor

You need a H-bridge and a SR-flipflop. Each button is connected to each sr-input, just do a couple of test so that you have the corect button connected to the correct input of the .SR. Then it should be easy to connect each output to the two inputs of the H-bridge.

Example design of H-bridge:
**broken link removed**

Because you ar most likely to have easier access to NPN transistors than NPN, you might like having a bridge that uses only NPN transistor (see attachment).

The easy circuit I attached has following benefits over the other one:
- Doesn't require PNP transistors
- It won't shortcircuit as long as you have done it right (and both transistors is functional).
- If you aplies either low signal or hig signal on both inputs (when they are connected in a H-bridge configuration) the motor will stop.

However the drawbacks is:
- The motor wont get the same voltage as Vcc. The voltage over the motor will be at least 1.2 volts below Vcc. The more current the motor draws, the more the voltage will drop.
- If you try to use darlington transistor for the upper one, then the voltage will drop aditional 0,6 volts.

 

[mvagusta]

Thanks for the quick reply! But i don't think the circuits are what i'm looking for tho, unless i'm reading it wrong?

The main thing i need is a circuit that switches the polarity of a voltage at each push of a single input.

 

[Prototyp_V1.0]

... The main thing i need is a circuit that switches the polarity of a voltage at each push of a single input.

Ok - then I guess the problem is like this: You have all the circuit's that is needed, but you don't know how to assemble it:

Well - I can draw it in almost no time.

 

[mvagusta]

Ahh, you are 100% correct Thanks for all the answers, you're awesome! But my stupid questions continue...

stupid question number 1: i'm pretty sure all the 3 voltage supply pins can be shorted together, true?

and number 2: what is the box on the left with the 4 pins: s, r, q & q?

I thought i knew more than this about circuits

 

[Prototyp_V1.0]

I cannot find any stupid question here

1)
Yes, the two power supplies might be the same. But it depends. The motor might require a different voltage than the SR latch.

2)
I'll post some links here and you HAVE TO READ the contents of the places - otherwise you'll most likely not understand the consept.

A SR latch is a digital circuit that can remember a state. There is two common ways to design a sr-latch. The most usual is to use two nand gates. But it can also being done with two nor gates.

In this case, most of the time both inputs of the sr-latch will be true (same as voltage on) because of the resistors, therefore you must chose the sr nand latch.

When designing your circuit, you can chose three different types of ways to make the SR-latch:

TTL
There is more than hundred different logic circuits. The one you need is the 7400 that contains four nand gates. What is important to remember about TTL circuits is that the power suply MUST BE 5 VOLTS. If not, it sure won't work, and in worst case, you'll burn the chip.
What more is that all inputs reads 1 (voltage on) when it's not connected. But the two resistors should be there any way, just in case. The output is often open collector. That means you have to make use of two extra pull up resistor.

Cmos
There is also cmos-logic circuits to find that does the same as ttl-circuits. The main difference of the ttl-circuits is:
- The voltage range is from 3 to 15 volts (ttl can just operate when Vcc=5 volts)
- All inputs that is not connected should be grounded to avoid damage.
- Care should be taken when handling those circuits to avoid damage caused by ESD.
The circuit you need is **broken link removed** that is four nand gates. Be aware of different pinout than the equivalent ttl-chip.

Diode transistor logic
This way you can design you own logical gates using simple transistors, diodes and resistors. This is the way to do it if the only electronic component source nearby is an old television, wich is not likely to contain any ttl or cmos gates.
There is advantages and disadvantages over ttl/cmos:
+ There is little or no risk for ESD damage.
+ You can use almost all kind of transistors, and diodes - and the value of the resistors can be almost anything - from 100 ohms maybe to 1Mohm. In your case the output resistor should not be very high (Guess max value around 2,2Kohm) because that same resistor shall make the transistor in the h-bridge to saturate, wich need some current to the base.
+ For a nand-gate, there is theoretically no limit how many extra inputs you can add.
* The maximum operating voltage is limited to the transistor that have the smallest operating voltage - or diode that have the smallest inverse voltage it can stand.
- The chematic will be more complex because of the extra number of components. Here you'll have seven small components instead of one 8-pin chip.
- A DTL-circuit will draw more current that a ttl or cmos, and that will affect lifetime if a battery is the powersource.
- The speed is a lot slower than a ttl-circuit, but this won't affect your project. Reason is that you might chose either a slow diode or a slow transistor (ex those designed for audio).[/b]

[edit]
Some of the links doesn't displays correct. Those you have to copy and paste into the adress field in your browser. I guess it's some bug in this forum.

 

[mvagusta]

Your help on latches is most excellent As you can tell i've had very little experience with them, and i will read all of the links.

Thanks again, i'll be right now

 

[zawmintun1]

Beautiful