Simple Circuit Help.....

Hi,

This could wll be the place to answer (almost) all of my problems...

I have a problem that im sure could be solved by some electronics genius out there. Basically i need a circuit that has 6 illuminated momentary pushbuttons as inputs, each one with 12v illumination. The outputs need to be 6 x 12v relays, one for each button.

OK so far... the snag is that the outputs need to be momantary (about 1 second) but the illumination needs to latch constantly on the selected button until another one is pressed.

The circuit is to extend the front panel of a seamless AV swithcher to anti vandal illuminated pushbuttons. I can interface the relays into the switcher but I would like the anti vandal buttons to be illuminated too, hence my problem.

I have found a circuit where the output relays latch until another button is selected however this has adverse effects on the reliability of the switching.

I can use Eagle to turn schematics into boards, im just not too bright when it comes to design!

I hope that someone out there can shead some light onto this for me (no pun intended)

Cheers,

Joel.

Use a PIC (or other micro-controller), a single cheap chip and a little programming will soon sort you out!.

Do I understand that when any button is pushed, all 6 outputs go high for one second but the selected (pushed) output stays high until another button is pushed?

Hi Russlk...

Just to clarify, when any of the 6 buttons is pressed,only its associated (relay) output goes high for one second, however the illumination on the button that has been pressed stays on until another button is pressed.

Basically its so that from a glance it can be seen from the buttons which one was last selected as it will be lit up however the relay on the output will have only activated for one second.

I hope this clears it up - i appreciate that for those of you who understand what your doing then suggesting PIC's etc may be obvious, not being quite as clever as this, what i could really do with is a working schematic.

Cheers.

jhauxwell said:

I hope this clears it up - i appreciate that for those of you who understand what your doing then suggesting PIC's etc may be obvious, not being quite as clever as this, what i could really do with is a working schematic.

Click to expand...

A schematic wouldn't help you much?, the whole point of doing it with a micro-controller is that the schematic is EXTREMELY simple - it's the code you write for the micro-controller that is the clever bit!.

Hi Nigel,

Thanks for your replies - i accept what you say about the simplicity of a PIC however you have pointed out my stumbling block - the code....

I posted my problem on this forum as a way of seeking assistance - i have limited knowledge, certainly not enough to figure this out for myself. If you or someone else who has the required knowledge is willing to help me with the code then that would be really appreciated.

I will continue googling to try and find out what i can.

Cheers.

jhauxwell said:

Hi Nigel,

Thanks for your replies - i accept what you say about the simplicity of a PIC however you have pointed out my stumbling block - the code....

I posted my problem on this forum as a way of seeking assistance - i have limited knowledge, certainly not enough to figure this out for myself. If you or someone else who has the required knowledge is willing to help me with the code then that would be really appreciated.

I will continue googling to try and find out what i can.

Cheers.

Click to expand...

Yeah, Nigel's solution with a pic is a common one on the forums here... If you have the time to learn programming, maybe this is a good solution. Most people do NOT know pic programming and sometimes the pic solution doesnt make sense for the time neeeded to invest in that learning curve. If you are looking for a soultion within 1 day, learning a pic solution is not the right answer.

Optikon said:

Most people do NOT know pic programming and sometimes the pic solution doesnt make sense for the time neeeded to invest in that learning curve. If you are looking for a soultion within 1 day, learning a pic solution is not the right answer.

Click to expand...

If you're doing electronics in the 21st century you NEED to know micro-controllers, and the PIC is the most popular (and easy to use?) of these.

Such a simple project doesn't require much programming, you could soon learn it in a few days - notice that no one has yet posted a hardware example!.

PIC wise, to keep it simple, you need 6 input lines (for the switches), six output lines (for the lamps), and 6 output lines (for the relays), a total of 18 I/O lines (6 in 12 out). So I would suggest something like the 16F876, a 28 pin PIC.

jhauxwell said:

I hope this clears it up - i appreciate that for those of you who understand what your doing then suggesting PIC's etc may be obvious, not being quite as clever as this, what i could really do with is a working schematic.
Cheers.

Click to expand...

A clock source is generated by the 555 timer, or if AC is available, the rectified 50Hz(=100Hz) can be used as a clock source instead so no 555 timer needed.

The 4017 is RESET upon power up and stays at Q0 state. Notices that its enable pin is pull HIGH so it will not count. As soon as a push button is press, the enable pin is pull low and the 4017 start counting. The clocking frequency has to be fast or else the lamp/relay would starts to operate.

The 4017 will stop counting when it reaches the output on which the push button is pressed. Its logic HIGH output will then drive the lamp driver and relay circuit. There is a capacitor at the relay driver PNP darlington transistor base pin therefore the relay will only be on for a brief moment and then released. The timing is controlled by the value of the capacitor.

I hope this circuit serve your purposes. If you need part values, just ask.

Eblc1388, nice! I think you need to move R1 or C1, though.

Ron

Ron H said:

Eblc1388, nice! I think you need to move R1 or C1, though.

Ron

Click to expand...

Yes, my mistake. Capacitor C1 should be connected to 555 timer pin6 and 0V instead.

Thanks Ron.

Hi,

I really appreciate the drawing - as offered, would you be able to put values/codes to the components that are missing them including the PNP Darlington junction, and the MOSFET and if you could also suggest a value for C2 to provide around a 1 second timing that would be great.

I appreciate your description too, from it i can understand how the circuit operates and that is important to me if i am to learn anything.

Cheers,
Joel.

jhauxwell said:

I really appreciate the drawing - as offered, would you be able to put values/codes to the components that are missing them including the PNP Darlington junction, and the MOSFET and if you could also suggest a value for C2 to provide around a 1 second timing that would be great.

Click to expand...

The n-ch MOSFET can be any suitable type with current of a few amps or more. This also applies to the PNP darlington. The problem with typical part numbers is I don't know where you are located and sometimes it makes a big difference.

You can select them from catalogue of your local component shop and post back the part number if you are not sure if it would fit.

Usually the schematic would not show power supply pins connections and decoupling capacitors. You have to get the datasheet of these ICs from the internet and connect them up correctly. Remember to add 0.1uF capacitor across each IC's positive and negative supply pins, as close to them physically as possible.

Hi,

Thanks for the reply - i tried to find the MOSFET you suggested in the diagram but i couldnt find it anywhere. I think i found an alternitave, its a IRL510 - RS part number 189-0438. Would this one work?

Cheers,

Joel.

Yes, but this one 40% the cost of IRL510.

RS:485-9159 N channel power MOSFET,IRF620 4A 200V