1 sec ON when High (3V), 1 sec OFF when low (0V) - no relay!

[Ibob]

Hi guys,
I have a Ethernet controller which I can control to switch on or off different channels.
When a channel is ON, it gives 3V constantly on the respective exit. When OFF - 0V constantly.
I want to wire it to a hand remote control, which switch radio receivers in order to remotely operate bulbs for example.
The remote control has buttons for ON OFF each receiver. They should be pressed momentarily.
The ON and OFF buttons on the remote have common wire and the other end connects to the ON or OFF wire respectively.
What I need to build is a circuit that connects the common wire of a button to the ON wire for a second when 3V, and to the OFF wire for a second when 0V at the exit of the controller.
I imagine some circuit with transistors and/or with timer(s) 555 but I cannot produce it without help I am afraid. Any ideas? A! I don't want to use relays.

 

[MikeMl]

Questions: Can the ethernet controller share a common ground with the remote control transmitter? If not, you will need to use opto-isolators.

What is the voltage across the push-button(s) when the button is not pushed as measured with a high-impedance input DMM?

If you put your DMM into DCmA mode and you connect the DMM leads across the (open) push button, how much current flows?

 

[cowboybob]

I've used many 2N2222 NPNs, with low voltage triggering, for low current manual switch interfacing, such as below:

As noted, R1 and R2 will need to be adjusted for your application to acheive saturation .

And, generally, grounding issues between a hand held, battery operated remote and another power source (such as the Ethernet device) are not a problem with a simple circuit like this.

 

[MikeMl]

What is special about 2N2222 for this application? Wouldn't any small-signal or switching NPN work as well?

 

[Ibob]

Hi,
Thanks MikeMl, I will answer your questions in couple of days when back home from my vacation.
Thank you cowboybob as well.

Meanwhile, let me add here that I am planning to supply the hend held remote with the same 12v adapter the Ethernet controller is supplied. I hope then the common GND would not be a problem. However what I know for the controller exits that they are directly connected to the main chip and i need to be sure i will not damage it somehow.

Cowboybob, maybe I am now klowledgable enough but I can't see how tge transistor will switch the ON button for 1 second, and how the same transistor will switch the OFF button for 1 second. I need only 1 second switching because otherwise the remote would continiously send the RF signal to the receiver.
So, when 3.3v - switch for 1 sec button 1, when 0v - switch button 2 for 1 sec.
These 3.3 or 0v are constant signals.
Please see the buttons on the diagram at my first post.
Cheers!

 

[cowboybob]

What is special about 2N2222 for this application? Wouldn't any small-signal or switching NPN work as well?

Mike,
Nothing special about the 2N2222, except that they're just so readily available and cheap (and a very easy number to remember ).

Ibob, I did not realize you were trying to trigger both hand held switches with just one trigger. Since you said that:

I have a Ethernet controller which I can control to switch on or off different channels.

(my emphasis on the plural)
I assumed you meant to use two outputs from the Ethernet controller to trigger two separate transistor switches.

Since what you need are, in essence, are two closures, or two negative going pulses to trigger the hand held device, obviously the simplest solution is two driving triggers.

If you only have the one trigger, the solution is considerably more complex.

So my question is; can you dedicate two outputs from the Ethernet controller to this task?

 

[Ibob]

...
So my question is; can you dedicate two outputs from the Ethernet controller to this task?

I'm afraid I cannot, i.e. I want to use all the channels available (16), so I will go with the complex solution

How about a circuit with 2 transistors, or more.. One of them will switch momentary the ON button when 3v, the other one will switch the OFF button momentary when 0v?
Or some timers, e.g. 555/556 could be used?
We can use the 12v supply available anyhow..
I have seen a lot of nice 555 circuits, but nothing like this I want.
Thank you for your time.

Check out these:
http://www.bowdenshobbycircuits.info/page9.htm#555-T.gif
Something like
Bistable Flip Flop
But maybe with optocouplers instead of the leds? I am not sure..


Cheers!

 

[Ibob]

Another idea: can use an invertor connected in parallel with the exit so that i will have 3v when exit is high, and another wire on the exit of the invertor when the exit is low?
However I don't have a clue about invertors, etc...

 

[alec_t]

Something like this perhaps?

When the Ethernet output goes to 3.3V the OFF line is pulled low (to ground) for ~0.8 sec then reverts to high (3.3V).
When the Ethernet output goes to 0V the ON line is pulled low (to ground) for ~0.8 sec then reverts to high (3.3V).
This situation can be modified by reversing the polarity of diodes D3,D4 if required.
If the CD40106 output sink/source current is inadequate its outputs could be buffered.

 

[Ibob]

Hi MikeMl, thank you for your questions, here are the answers:

Questions: Can the ethernet controller share a common ground with the remote control transmitter? If not, you will need to use opto-isolators.

I am not sure. Maybe someone can tell me better? I am planning to use the same 12V supply for both, the Ethernet controller and the hand held remote control. Hope it will not be a problem.

What is the voltage across the push-button(s) when the button is not pushed as measured with a high-impedance input DMM?

4.6V

If you put your DMM into DCmA mode and you connect the DMM leads across the (open) push button, how much current flows?

2mA and when I measure it switches the button! The LED starts blinking as it is pressed.

 

[Ibob]

Something like this perhaps?
View attachment 73340
When the Ethernet output goes to 3.3V the OFF line is pulled low (to ground) for ~0.8 sec then reverts to high (3.3V).
When the Ethernet output goes to 0V the ON line is pulled low (to ground) for ~0.8 sec then reverts to high (3.3V).
This situation can be modified by reversing the polarity of diodes D3,D4 if required.
If the CD40106 output sink/source current is inadequate its outputs could be buffered.

Hi alec_t,
That's very very close to what I am after I guess.
The problem is I have some issues fully understanding it, e.g. what the D3 and D4 to connect to in order to trigger the buttons?
Why are the other diodes?
I think I need a bit different logic than the one described here...
I need when Ethernet controller output goes to 3.3V the OFF line to be high for not more than 1 second and then to revert to low.
When the Ethernet controller output goes to 0V, the ON line to be high for not more than 1 second and then to revert to low.
I liked very much this CD40106 invertor IC.

Can I also think of using some MOSFETs here... one per each line - for ON and for OFF lines?
So far I think of splitting the Ethernet output into 2 wires, the one to be inverted with CD40106 inverter, and both of them to continue to the MOSFET switches... that should simulate button press for less than one second somehow...

I will better understand if I see it as a circuit... with the buttons and with everything...
Thanks so much for your time.
Cheers!

 

[MikeMl]

Hi MikeMl, thank you for your questions, here are the answers:

Can the ethernet controller share a common ground with the remote control transmitter? If not, you will need to use opto-isolators.

I am not sure. Maybe someone can tell me better? I am planning to use the same 12V supply for both, the Ethernet controller and the hand held remote control. Hope it will not be a problem.

Check it using your DMM in Ohms mode. With the remote control transmitter unpowered (battery removed, but power switch on), measure the resistance between each side of the push buttons to where the positive and negative poles would be if the battery was there (Total of eight measurements; some should show a "short" of less than 1Ω).

I'm trying to determine if we need high-side or low-side transistor switches wired across the buttons. Also these measurements will tell us if it is ok to connect the battery negative to the negative of the 12V that powers the controller.

 

[alec_t]

The diodes are so that the lines which the buttons control can be pulled low (or high, depending on diode orientation) but allow for any internal pull-ups/downs internal to whatever the buttons control.

I will better understand if I see it as a circuit... with the buttons and with everything...

Are the buttons active Low or active High, i.e. do the buttons at present short something to ground when pressed, or raise something to 3.3V (or whatever) when pressed? That will determine what type of MOSFET (p- or n-) would be suitable.

 

[Ibob]

The ON and OFF lines on the remote are connected directly to GND.
Each channel has ON and OFF buttons, which have a common high point (4,6v).
They are active low as they are shorting to GND when pressed.

 

[alec_t]

If I've understood you correctly then this revised circuit should do the trick:


And here's a waveform plot:

 

[Ibob]

alec_t - thank you so much!
It seems that will work. I will test it when I get the parts and post the results.
Could you be so kind to explain what the 1st, 2nd and 3rd inverters are doing exactly for the ON line and what the 1st and 2nd inverters are doing for the OFF line, e.g. how the signal changes (and the duration) after each inverter. I just follow hardly the waveform.
I am asking because I see too many invertors, but I cannot get why for?
Cheers!

 

[alec_t]

The CMOS gates used have the advantage of an extremely high input resistance, so require negligible current to turn them on or off (unless switched rapidly), unlike BJT transistors. Thus they can be used as buffers. That means we can use smaller value capacitors and higher resistance values for our timing than would be needed for driving BJT transistors directly, and also means less loading of the Ethernet output. When 'In' goes high C1/R1 generate a positive pulse. This is inverted by U1d then inverted back again by U1e (because we didn't really want to invert the pulse; only buffer it) to switch Q2 on and hence make 'OFF' low. Similarly, U1b and U1c together act as a non-inverting buffer. However, we do use U1a as an inverter (as well as a buffer), so that when 'In' goes low U1a output goes high and C2/R2 generate a positive pulse which via buffer U1b/c turns on Q1 to make 'ON' low.

Edit: Be aware that CMOS circuits are easily damaged by static electricity. Take due anti-static precautions.

 

[Ibob]

Hi alec_t,
thanks for the details, now I see.
However, I think U1a should be on the OFF line and not on the ON line. The Ethernet signal will be high when button ON should be pressed and low when the OFF button should be pressed. But thats easy to change of course as this is the only difference between the two lines.
thanks again so much, I will post the results when i do the test.

 

[alec_t]

You don't need to move U1a. Just swap the labels 'ON' and 'OFF' on the schematic

 

[Ibob]

If I've understood you correctly then this revised circuit should do the trick:
View attachment 73390

Hi alec_t,
Now I have all the parts and I will assemble it.

Just wanted to check again with you, these caps, why they are connected that way and not in paralell with the power?
I was expecting to see the R and C positions the opposite?

Also, what exactly the diodes are doing?

Thanks!