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 Forum index » DIY Hardware and Software » The layout factory
How to make a momentary connection ?
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rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Sat Nov 30, 2013 1:29 pm    Post subject: How to make a momentary connection ? Reply with quote  Mark this post and the followings unread

I will try to explain:
I do not know how to formulate it, so I was not even able to google for any circuit or component.
Let's say it is like connecting 2 points (here a CMOS component) via a push button, but instead of the a OFF/(ON) push button I have to use a pulse signal.
I have the circuit with my CMOS and my pulse signal too, but I ignore how to make this pulse "connect" the 2 points of my CMOS (pin 1 and pin 16) momentarily. I guess I need only a component ? Transistor, diode ? Thank you very much !!!!
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PHOBoS



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PostPosted: Sat Nov 30, 2013 1:37 pm    Post subject: Re: How to make a momentary connection ? Reply with quote  Mark this post and the followings unread

The industrial way would be the use of a mechanical relay but that's for high current stuff. In your case a transistor might do or a CMOS switch like a
CD4016/4066. I've used optocouplers myself, which is great if you want to keep circuits completely isolated from eachother. But if it's a digital signal
something simple as an AND gate can do the trick, it would even be possible with just a diode and a resistor. It all depends a bit on the signal you want to switch.

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rogerlatur



Joined: Dec 22, 2012
Posts: 118
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PostPosted: Sun Dec 01, 2013 8:07 am    Post subject: Re: How to make a momentary connection ? Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
The industrial way would be the use of a mechanical relay but that's for high current stuff. In your case a transistor might do or a CMOS switch like a
CD4016/4066. I've used optocouplers myself, which is great if you want to keep circuits completely isolated from eachother. But if it's a digital signal
something simple as an AND gate can do the trick, it would even be possible with just a diode and a resistor. It all depends a bit on the signal you want to switch.

I want to make a very brief contact between two pins on a CD4029, by sending a pulse signal from a sequencer. As I ignore how to make them briefly enter in contact together on pulse signal (open and close a connection briefly), I thought I would ask here.

"Relay contact" might be the term I did miss. A relay acting like a momentary switch (connecting 2 pins of a CD4029) on incoming pulse.
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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Mon Dec 02, 2013 11:43 pm    Post subject: Re: How to make a momentary connection ? Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
In your case a transistor might do or a CMOS switch like a
CD4016/4066.

Thank you PHOBoS ! I will check it.
I have to find a way to make the switch momentary, without sending a second pulse to "switch off".
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DES



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PostPosted: Wed Dec 04, 2013 8:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

What is the chip whose pins you are trying connect? Would be easier to give more precise ideas.... What type of signal is going thru the connection or is it switching a static voltage or ground?
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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Tue Dec 10, 2013 5:56 am    Post subject: Reply with quote  Mark this post and the followings unread

DES wrote:
What is the chip whose pins you are trying connect? Would be easier to give more precise ideas.... What type of signal is going thru the connection or is it switching a static voltage or ground?

I am trying to reset a sequencer via pulses, and it was not built with any reset possibility. The only way I found was to try out within the different chips on the board as I read on the datasheets of some of the CMOS used on the circuit that they have a reset input. The only way I found to reset it was trying out all pins without success. But by connecting pin 1 and pin 16 of CD4029 very briefly, the sequencer starts back from step 1.
This is the reason why I asked here, as I am also interested in knowing how to switch briefly more generally.
I will try with a transistor, hoping that I do not kill the CD4029.
Learning by doing ...
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DES



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PostPosted: Tue Dec 10, 2013 7:36 am    Post subject: Reply with quote  Mark this post and the followings unread

I found a data sheet for the 4029 here:
http://www.sycelectronica.com.ar/semiconductores/CD4029.pdf

Pin 16 is Vdd or your positive supply voltage to the chip....by connecting pin 1 to pin 16 ( or Vdd ) you reset the chip counter. You can manually do this with a momentary switch, a CMOS logic gate ( AND, OR, NOR, ETC...) or any other CMOS logic output or a transitor switch, etc. For example, you could have a BCD decoder matrix setup connected to the 4029 outputs so that when it reached a certain programmed number it would send a logic high signal to pin 1 to reset the counter back to zero or connect it to pin 10 to change direction. The chip has several modes of operation you can explore. A lot would have to do with how it's already connected. Looks like a fun chip to mess with Smile

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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Tue Dec 10, 2013 9:07 am    Post subject: Reply with quote  Mark this post and the followings unread

DES wrote:
Pin 16 is Vdd or your positive supply voltage to the chip....by connecting pin 1 to pin 16 ( or Vdd ) you reset the chip counter.

Exactly. I thought then that my pulse, sent to pin 2 would do the same as getting current from Vdd, which is obviously wrong as it doesn't react then.
I even amplified the pulse signal without success. I still need to learn further!

I found these pages:
http://www.rason.org/Projects/transwit/transwit.htm
and I will need to re-read again because I did not understand the calculations (load etc). But these pages look very helpful to understand how it works.
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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Tue Dec 10, 2013 9:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Do you know what means "To Load" on this circuit taken from here?
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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analog_backlash



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PostPosted: Tue Dec 10, 2013 9:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rogerlatur.

The label "to load" just means to the part of the circuit which will be drawing a current from the transistor. Looking at what you're trying to do, I would try pulling down pin 1 to ground with a 100K resistor and also connecting pin 1 to the collector of the 2N3906. Hopefully, when you send a pulse into R1, you should get a momentary 12V(ish) at pin 1 and the 4029 should reset.

I hope that works!

Gary
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rogerlatur



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PostPosted: Tue Dec 10, 2013 9:50 am    Post subject: Reply with quote  Mark this post and the followings unread

analog_backlash wrote:
Hi Rogerlatur.

The label "to load" just means to the part of the circuit which will be drawing a current from the transistor. Looking at what you're trying to do, I would try pulling down pin 1 to ground with a 100K resistor and also connecting pin 1 to the collector of the 2N3906. Hopefully, when you send a pulse into R1, you should get a momentary 12V(ish) at pin 1 and the 4029 should reset.

I hope that works!

Gary

Hi Gary
Here is what I drawn before I saw your post.
I will now compare to your post.


2N3904_switch.jpg
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2N3904_switch.jpg


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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Tue Dec 10, 2013 9:54 am    Post subject: Reply with quote  Mark this post and the followings unread

I forgot resitor at 1.
Will add resistor between pin 1 and ground.
Will also change from NPN (2N3904) to PNP (2N3906) then.

I guess I also need to swap between collector and emitter !
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analog_backlash



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PostPosted: Tue Dec 10, 2013 10:19 am    Post subject: Reply with quote  Mark this post and the followings unread

I was thinking of something like this:


Reset Idea.jpg
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rogerlatur



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PostPosted: Tue Dec 10, 2013 10:54 am    Post subject: Reply with quote  Mark this post and the followings unread

analog_backlash wrote:
I was thinking of something like this:

Very cool ! I was not sure about NPN or not. Thank you very much !
I will try this.
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gdavis



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PostPosted: Tue Dec 10, 2013 11:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Assuming pin 1 is simply grounded in the original circuit, you really don't need a "switch" here.

You probably just need to pull pin 1 down with a resistor to ground (if the reset input isn't permanently connected) and connect your reset pulse input directly to pin 1. Make sure pin 1 isn't connected directly to ground, otherwise you'll be creating a short.

The transistor circuit above is "buffering" in the input, which isn't necessarily a bad thing, but with a large pull-down resistor (e.g. >= 100k) you should have no problem driving it directly without a buffer.

You really don't want to think of this as "connecting two points of the chip together" when one of those points is VDD. You should be thinking of it as driving the preset input either high or low (active or inactive state).

"Connecting two points" implies passing a signal from one point to the other which isn't really what you're doing between pin 1 and pin 16.

You could say that's a semantic argument, and maybe it is, but this would be more typical of how we would explain what is going on here. Part of the "language" of electronics if you will.

Having said that, you may have an issue with the timing of the pulse depending on the circuit, but that's a whole other discussion Wink

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rogerlatur



Joined: Dec 22, 2012
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PostPosted: Tue Dec 10, 2013 12:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

I tried the circuit with the 2N3904 and it works. the pulse resets now the sequencer.

gdavis wrote:
You probably just need to pull pin 1 down with a resistor to ground (if the reset input isn't permanently connected) and connect your reset pulse input directly to pin 1. Make sure pin 1 isn't connected directly to ground, otherwise you'll be creating a short.

I tried before asking here all kind if things (...) and blew already another chip in the circuit making a short.
I did not know about the resistor between pin 1 and ground to protect from shorts ! Thank you very much for the advice, I will try what you suggest without the use of the transistor.
Also thank you for your clear explanations !!!
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rogerlatur



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PostPosted: Tue Dec 10, 2013 1:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

rogerlatur wrote:
gdavis wrote:
You probably just need to pull pin 1 down with a resistor to ground (if the reset input isn't permanently connected) and connect your reset pulse input directly to pin 1. Make sure pin 1 isn't connected directly to ground, otherwise you'll be creating a short.

I tried before asking here all kind if things (...) and blew already another chip in the circuit making a short.
I did not know about the resistor between pin 1 and ground to protect from shorts ! Thank you very much for the advice, I will try what you suggest without the use of the transistor.
Also thank you for your clear explanations !!!

I just tried with pulse to pin 1 and pin 1 connected to ground via 100k resistor. The sequencer just stops. I guess it depends how all pins are connected in the circuit and what pin 1 already does or not, which is impossible for you to know without the circuit details !
But no problem, as it works properly with the switch.
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analog_backlash



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PostPosted: Tue Dec 10, 2013 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi again,

Glad that the circuit worked - I thought that it would. Actually, as gdavis has said, it should work without the transistor. I didn't think of that at the time, I was just thinking about how to get the transistor to work!

Connecting pin 1 to ground or +12V without the resistor should not have destroyed the chip (I've certainly built circuits with a 4029 pin 1 straight to ground). What the resistor is doing is pulling the pin to ground for most of the time (input pins shouldn't be left floating), but allowing it to be taken up to the higher voltage when needed (you cannot connect +12V directly to the 0V rail).

By the way, there may be a point in using a transistor to "switch" the input. I asked PHOBoS once why he often uses transistors in this kind of circuit and one of the things he said was that it would allow the circuit to be triggered by another circuit using a different voltage e.g. +5V from a microcontroller circuit.

Gary
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batchas



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PostPosted: Tue Dec 17, 2013 11:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Interesting thread!
I registered on the forum after reading this, because the solution shown by analog_backlash with the transistor is exactly the solution I chosed a couple of months ago to reset a sequencer too, a flopSeq v1, after I tried to reset without success directly with resistor to ground and skipping the transistor.

The flopSeq circuit uses a 4013 but also a 4029 and I reset the sequencer via pin1 of 4029 because it reacts better than using reset pin4 or reset pin10 of 4013.

There are small issues which I'll have to live with at the moment, mounting last step as step1 on the panel as it restarts from step8 instead of step1. Which also means that the minimum number of steps in a loop is 2.
Demo here

For rogerlatur:
If you are using the first original flopSeq circuit like me, you can use a 1 pole / 8 pos rotary switch to reset the sequencer via the pulses from the + poles of the LEDs. You can also use the same pulses to get single switchable pulse outputs which also do not exist on this version on the flopSeq. Let me know if you need me to explain.
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