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Current`s direction reversal after a certain interval

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imperatormk

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Hey,

I need to make a simple device which will change the current`s direction after a certain interval (i.e 5 seconds.).

Can you give me some idea or scheme of it`s construction? (Something with 555 timer would be OK.)

Thank you in advance...
 

What do you mean by "change the current's direction"?
If any current in any part of a circuit will meet your needs, then you could just join 2 resistors in series between a positive power rail and another supply rail at half the supply volts. Connect the collector of a transistor to the mid point of the resistors, and the emitter to 0 volts.
Keep the transistor off, and current flows from the high rail through both resistors to the half-voltage rail.
Turn the transistor on, and current reverses through one of the resistors.
 
DXNewcastle said:
What do you mean by "change the current's direction"?
If any current in any part of a circuit will meet your needs, then you could just join 2 resistors in series between a positive power rail and another supply rail at half the supply volts. Connect the collector of a transistor to the mid point of the resistors, and the emitter to 0 volts.
Keep the transistor off, and current flows from the high rail through both resistors to the half-voltage rail.
Turn the transistor on, and current reverses through one of the resistors.
Click to expand...

Hmm, I need it to be automatic. I found something that might work? Would you be so kind to take a look of it and tell me your opinion?

The 555 Bistable Circuit - Electronics in Meccano (Figure 2: The 555 Bistable Circuit) Note: it`s not automatic, but it`s a good start

If it isn`t OK, can you provide me some scheme that might meet my needs?
 

Its not clear what you mean by 'automatic', usually there is some causal or otherwise programmed and designed circumstances which preceed an event, but I'm sure you can implement something that behaves in the way you want. A 555 timer introduces a delay to a trigger and the datasheet you've linked seems reasonable.

The part I was trying to help you with was 'changing the direction' of a current. You could connect the output of a 555 timer to the transistor I referred to and achieve a current reversal across one of the resistors when the transistor was turned on/off by the timer (or other 'automatic' generator of a voltage change).

Does that get you any further forward?
 

DXNewcastle said:
Its not clear what you mean by 'automatic', usually there is some causal or otherwise programmed and designed circumstances which preceed an event, but I'm sure you can implement something that behaves in the way you want. A 555 timer introduces a delay to a trigger and the datasheet you've linked seems reasonable.

The part I was trying to help you with was 'changing the direction' of a current. You could connect the output of a 555 timer to the transistor I referred to and achieve a current reversal across one of the resistors when the transistor was turned on/off by the timer (or other 'automatic' generator of a voltage change).

Does that get you any further forward?
Click to expand...

I get it. Now I need *timer* or something to turn on/off the transistor. Thank you for the clear up.
 

OK, I found something that is based on 555 timer and DPDT switch. Here is it`s scheme:

ImageShack® - Online Photo and Video Hosting

reverse-device.gif (Click to enlarge)

But I have one question. I am not sure how to wire the 555 timer output wires with the DPDT relay, so some help would be useful...
 
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imperatormk said:
I am not sure how to wire the 555 timer output wires with the DPDT relay, so some help would be useful...
Click to expand...
You have to explain what you want to connect to the relay's outputs before anyone can give you the full answer, but this might help to get you started . . .
The diagram correctly shows a timer driving a trnsistor which is then connected to the coil of the relay.
The diagram has assumed that one Normally Closed (n/c) contact is connected to +13 volts and the other n/c contact is connected to 0 volts.
It also shows that one of the Normally Open (n/o) contact is connected to 0 volts and the other n/o contact is connected to +13 volts.

Is anything still unclear?
 

DXNewcastle said:
Is anything still unclear?
Click to expand...

So far nothing.

The relay`s outputs shall be connected to an electomotor which is going to change it`s direction after a certain interval (due to the changed current direction by the relay driven by the 555 timer.)

Correct me if I am wrong, but it should work fine.
 
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That is NOT a transformer. Check with your electronic symbols - you'll see that the curly / spiral is a coil. If it was a transformer, then there would be at least two coils, a primary and a secondary winding. The coil is the part of the relay which really is just that, a coil, and when current passes through it it creates a magnetic field which operates the two mechanical DT switches.

The red and blue dots represent the switch contacts: the red ones are the Normally Closed contacts (n/c), the blue ones are the Normally Open contacts (n/o), and the two with black lines drawn out to the right (labelled OUT) are the moving contacts - these are the connections which simultaneously switch over from contact with the red terminals (when the coil is energised) to contact the blue terminals.

The part you've marked with the red rectangle is the whole relay.
Try energising the relay and see which connections are made and broken using a meter.
Also read my previous post in the light of this explanation and hopefully it will all make more sense.
 
Now it makes MUCH more sense. Thank you a million...

So, I am starting to assemble my device. If I run into troubles, I`ll post...

Thank you again...
 

So, I haven`t yet started assembling the device and I have a problem. As you can see in the diagram, the 555 timer`s pin numbers are mixed so the device can be assembled without any problems. However, the pin numbers on the real IC differ from them on the diagram, making it difficult to link the elements. I need some hint or suggestions since my experience is limited.
 

You might have to explain more about how you are physically arranging the components.
The position of the pin numbers on the IC are in a circle:-

1 8
2 7
3 6
4 5

You might have to explain what kind of board you are using to hold the components.
As you don't have much experience, can I suggest that you do NOT solder the IC onto the board, but instead, use an 8 pin socket. That will allow you to remove (and replace?) the IC later without having to solder & unsolder it.
 

I know the number positions but you can see that the numbers on the diagram differ from the numbers on the real 555 IC. I see that I need to connect the elements using narrow wires (depending on the location) and not as simple as on the diagram, where all elements are linked with straight lines (i.e. wires)

I am using something like this:

Google Image Result for http://media.digikey.com/photos/Vector%20Photos/8003.jpg

You might have to explain more about how you are physically arranging the components.
Click to expand...

I haven`t yet started, but I see that I can`t arrange them as simple as on the diagram for the reasons written above.

P.S. I don`t have experience of other type, but if I end up with having to unsolder the parts, I won`t have any troubles. However, I`d need something like step-by-step so as the assembly can go easier: (See below)


With the DC power off, wire positive power to pins 4 and 8 of the IC and ground to pin 1. Insert the resistor for Ra and wire one side to pin 7 and the other to positive power. Insert Rb into the board so that one side connects pin 7 and the other connects pin 6. Insert the capacitor so that one side connects to pin 6 and the other goes to power ground. Wire pin 2 to pin 6.
Click to expand...

So, if you can write something like the guide above (it`s is a good start, but it`s incomplete), I`d be very grateful.

Thank you.
 
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imperatormk
Yes, circuit drawings are drawn to illustrate the electronic and functional connections, not the physical package in which ICs are manufactured.

I strongly believe that you have to do this layout work yourself, otherwise we'll end up spending more time on the words and descriptions than on simply building the thing!
Just use bits of paper to draw it out in a few layouts that look good. As I guess you realise, its not critical where you physically place components as long as the wires connect everything that must be connected (and never connect anything that shouldn't be connected).

Remember that 3 of the components must be connected the correct way round: the diode and the 2.2uF cap have a positive and negative end. The transistor has 3 distinct pins, E B & C.
 

You are completely right :) I`ll start doing it and let you know if it works. :)

---------- Post added at 16:31 ---------- Previous post was at 15:36 ----------

OK, I assembled one part of the thing so as to see if the diode will flash when the output pulse goes high.

Wire the LED's anode to pin 3, its cathode in series with the resistor, and the other end of the resistor to ground. The LED will flash when the 555's output pulse goes high.
Click to expand...

However, the LED diode is on all the time, instead of ~1.5 secs on and ~1.4 secs off (according to the calculations). I have triple checked the connections, but I can`t find anything suspicious.

Here is the diagram (I am not sure if the LED diode on the diagram is positioned properly, but I know it`s OK because it works (all the time though)

ImageShack® - Online Photo and Video Hosting

modh.png
 
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Its so hard diagnosing faults with other people's circuits by internet forum. If we did this one step at a time like this, we'd probably be asking a question a day for 3 weeks.
If you'd like help, please give full data. In this case the minimum we'd need is the voltage on each pin of the IC which, we can compare with the datasheet and decide what is inconsistent with expectations, and an explanation if any of these voltages change over time. Better still, the results of several investigations at once.
But "the LED diode is on all the time" doesn't provide anything we can work with. Sorry.
 

I feel you. I`ll measure each pin`s voltage and post it here. Sorry for not giving the necessary info.
 

...Now I feel like the biggest moron in the world. After a week of troubleshooting, I noticed that simply I was using UA741CN instead of CM555... 8O
 
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