Timer Switching Circuit

Thread Starter

sab201

Joined Nov 18, 2023
109
Good Day all,

I want to design the following circuit.

It consists of 3 circuits, Circuit 1, 2 and 3. Circuit 1 and Circuit 2 send output signals to Circuit 3. Circuit 3 only acts as a receiver and it does not need any control. I want Circuit 1 to send signal to Circuit 3 for 1 hour. Then I want Circuit 2 to send the signal to Circuit 3 for the next one hour. Then again it automatically switches to Circuit 1 and the cycle should repeat. Both Circuit 1 and 2 are ON all the time. Only the signal fed to Circuit 3 must swich ON and OFF and changeover every 1 hour.
sketch-1715792462001.jpgI have done some analysis and thought of using this relay module which has built in timer programs that can be used for this purpose.

71zlh8_5vfl._sl1500_083433f0-ba96-46c7-a1c9-bf969aa8567c.jpg
https://robocraze.com/products/dc-6...LzlyGNN4Ke63Qo9u1CvsyX1SOM7kFdVhoC5M4QAvD_BwE

But what I wanted to know is could there be any other simpler method that could be used for this automation.

Thanks
 

ElectricSpidey

Joined Dec 2, 2017
2,881
For those time periods I would say a programable relay is just about as simple as it gets.

From what I can gather from the instructions on that timer ad, the mode you need is available...but I caution you, I'm no expert in interpreting such instructions.

Just be aware that some relay contacts need a minimum current to perform properly over time.
 

AnalogKid

Joined Aug 1, 2013
11,196
You don't show a common ground between circuits 1 and 2, and circuit 3. This is necessary.

Also, what are the "signals"? Voltage / current / frequency - anything?

ak
 

Thread Starter

sab201

Joined Nov 18, 2023
109
You don't show a common ground between circuits 1 and 2, and circuit 3. This is necessary.

Also, what are the "signals"? Voltage / current / frequency - anything?

ak
Yes you are correct. Actually the grounds are common i am aware of it but I missed to mention it in the drawing. But that is correct to show that the grounds are common.

Here is the corrected circuit
20240516_100009_0000.jpg
The signal is voltage signal. I already mentioned it as Vout and Vin. They are at the range of 1 to 3 Volts DC.
 
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Thread Starter

sab201

Joined Nov 18, 2023
109
For those time periods I would say a programable relay is just about as simple as it gets.

From what I can gather from the instructions on that timer ad, the mode you need is available...but I caution you, I'm no expert in interpreting such instructions.

Just be aware that some relay contacts need a minimum current to perform properly over time.
Yes that one has this required program you are correct its also explained in this youtube video here


Using such a relay is what I wanted to avoid here especially the click sound if possible and it could get worn out along the run. I would like to use a proper "softer" timer. But I guess that wouldnt be for this switching time period.
 

Thread Starter

sab201

Joined Nov 18, 2023
109


Are these analog signals that must be switched precisely, or digital signals?

ak
These signals are - one is voltage waveform output from a 555 timer square wave generator which is Circuit 1 and other from a DDS signal signal generator which produces sine, square, triangle, sawtooth waves which can be chosen with a frequency selecting option which is Circuit 2. They need not be switched precisely nor the switching time matters. As long as the waveforms reach Circuit 3 once every hour changing between them that is fine.
 

AnalogKid

Joined Aug 1, 2013
11,196
A high-power relay such as the one in post #1 and #5 actually is inappropriate for low-level signals. It usually has silver-bearing contacts that require a small arc to keep them clean. However, those modules are such a low cost on ebay that it probably is worth a try.

Another way to go is with a much smaller relay with SPDT contacts (DPDT also is ok), something with a 5 Vdc or 12 Vdc coil; a 24-hour lamp timer from WalMart or ebay, and a USB power supply left over from a cell phone or camera. Select the relay to match the power supply output. Wire the signals to the contacts as in post #1, connect the 5 V supply to the relay coil, and set the timer to go on for 1 hour, off for 1 hour, repeat.

Where are you located?

ak
 

ElectricSpidey

Joined Dec 2, 2017
2,881
I don't know what your capabilities are but if you want to avoid using a relay you may be able to remove the relay from that module and drive some kind of semiconductor components such as...

CD4066
Transistors...etc.
 

Thread Starter

sab201

Joined Nov 18, 2023
109

Another way to go is with a much smaller relay with SPDT contacts (DPDT also is ok), something with a 5 Vdc or 12 Vdc coil; a 24-hour lamp timer from WalMart or ebay, and a USB power supply left over from a cell phone or camera. Select the relay to match the power supply output. Wire the signals to the contacts as in post #1, connect the 5 V supply to the relay coil, and set the timer to go on for 1 hour, off for 1 hour, repeat.

Where are you located?

ak
Ok I am starting to look for such 24 hour lamp timers online. Thanks for the information. I am in southernmost part of India, Asia. Here mostly all electronic components are readily available.
 

Thread Starter

sab201

Joined Nov 18, 2023
109
I don't know what your capabilities are but if you want to avoid using a relay you may be able to remove the relay from that module and drive some kind of semiconductor components such as...

CD4066
Transistors...etc.
That sounds like a good idea. When I remove the relay, I will have the supply points on the board where the IC supplies voltage to activate the relay. I can solder two wires to these points on the board and bring it out. Now in these wires I will have the activation ON/OFF signals every one hour. I have this much capability.

But I am not sure how to make a circuit to use these semiconductor devices for this switching purpose to replace the relay. It must be pretty simple (I suppose) would be great if you could advice how it can be done.

Thanks.
 

ElectricSpidey

Joined Dec 2, 2017
2,881
I won't have access to my other PC for an indeterminant amount of time.

But in the meantime... (and in case someone else wants to take a stab at it)

Can your circuit tolerate some series resistance between the signal generators and circuit 3? And how much if so?

What kind of load does circuit 3 present to the signal generators.

My first idea not knowing whether the relay coil is switched low or high side was to interface using an Opto-Coupler.
Then use that to drive some Schmitt inverters which in turn control a CD4066B.
With some delays to prevent both signals being present at the same time.

But if the circuit cannot tolerate the series resistance the 4066 inserts, then you would need MOSFETs instead.
 

Thread Starter

sab201

Joined Nov 18, 2023
109
ElectricSpidey,

That gets more bit complicated. I thought replacing relay with semiconductors would be easy but that doesn't seem to be the case.

But could this 2 channel solid state relay module available on market be used instead of the mechanical relay in that original timer module for this purpose.

5v-2-channel-ssr-g3mb-202p-solid-state-relay-module-240v-2a-output-with-resistive-fuse-800x800~2.jpg
https://www.electronicscomp.com/2-c...gmMaCL72WAk4NFD9SGhfiDiiMC8C2NyYaAukmEALw_wcB

The circuit cannot tolerate series resistance.

Edit: It is mentioned it is used for larger currents and also contains a resistive fuse could it be used for smaller current values.
 
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ElectricSpidey

Joined Dec 2, 2017
2,881
Yea, I could see some sort of dual SSRs working for you...perhaps not those, but the tricky part is switching between them.

Another question I meant to ask was...does your signal generator pull the output below ground?
 
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AnalogKid

Joined Aug 1, 2013
11,196
The dual SSR in #13 will not work for you. As you can see in the image, it is designed to switch 120/240 V mains power. Those devices probably have a TRIAC as the switching element, and the TRIAC forward voltage is equal to or greater than your entire signal.

Except for electro-mechanical relays, ALL switching devices will present a resistance or a voltage drop to the circuits. This is not a huge problem, just something to be dealt with. Of course, that requires knowing *everything* about the signals, their sources, and their destinations.

Source Voltage
Frequency
Waveform
Available Source Current
Source Output impedance
Destination Input impedance

etc.

The CD4066 is an OK analog switch for some applications where the destination circuit has a high input impedance, but it does insert a significant series resistance into the signal path. Per the datasheet, at 10 V it has a series resistance of 160 ohms typ. and 400 ohms max, and both of these values have a significant temperature coefficient. Of course there are other analog switches with way better performance.

ak

1715976687068.png
 
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Thread Starter

sab201

Joined Nov 18, 2023
109
ElectricSpidey and AnalogKid,

Thanks for all the information. I am trying to find a best possible solution so im looking into all available option. As for CD4066, I looked into its details and it has only Normally open NO contacts and no NC contacts. So when the timer sends a signal to the control pin of the ic, one switch can be closed at a time. I am not sure how this IC can be used for this application of switching over between two circuits like a relay.
 

ElectricSpidey

Joined Dec 2, 2017
2,881
ElectricSpidey and AnalogKid,

Thanks for all the information. I am trying to find a best possible solution so im looking into all available option. As for CD4066, I looked into its details and it has only Normally open NO contacts and no NC contacts. So when the timer sends a signal to the control pin of the ic, one switch can be closed at a time. I am not sure how this IC can be used for this application of switching over between two circuits like a relay.
Well, that is where the extra bits come in. (you would have the same condition if you were to use the relay in post #13) Of course it has already been explained why that relay won't work by AnalogKid.

And we have already determined that the 4066 presents too much series resistance.

If I were you, I would get the module you first presented, I would remove the relay and replace it with a small signal telecom relay with the proper gold contacts.

Of course, you never specified the load that circuit 3 presents.
 
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