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Need help with voltage flip flop please.

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goofy

New Member
Hello. I am trying to make a variable voltage flip flop circuit. But not the standard flip flop where you change polarity. I want to turn on one 24VDC device and then the other one with a time delay varrying from 1 second to 60 seconds.

I want 24VDC + and - input and then 24VDC + and - twice for the two outputs.

I have enough knowledge to construct a list of items to a schematic but that's about it. And Radio Shack is right next door. :)

Any help is appreciated. Thank You.
 

ljcox

Well-Known Member
goofy said:
Hello. I am trying to make a variable voltage flip flop circuit. But not the standard flip flop where you change polarity. I want to turn on one 24VDC device and then the other one with a time delay varrying from 1 second to 60 seconds.

I want 24VDC + and - input and then 24VDC + and - twice for the two outputs.

I have enough knowledge to construct a list of items to a schematic but that's about it. And Radio Shack is right next door. :)

Any help is appreciated. Thank You.
We need more information as to what you want to do. Your description is rather vague. For example what does "I want 24VDC + and - input and then 24VDC + and - twice for the two outputs" mean?

A diagram may help us to understand.

Len
 

goofy

New Member
I'm sorry. I will try to explain more.

I want to build a small box with 6 screw on wire connectors and a knob in the middle. Two of the connectors are on one side and connect to a supply of 24 volts dc current. The other four are for right and left, positive and negative for both, which output 24 volts dc alternatly with the speed controled by the knob in the middle.

Exact application is, I want to turn on one 24 volt dc sprinkler valve and then turn in off while turning on the another one, constantly repeating the sequence indefinately, but with the speed of the valve switching varrying from 1 second to 60 seconds, controlled by the knob (or VR).

I sure hope this helps because I could sure use it. ( The help that is! )

Thank you for your reply by the way. :)

Alan
 

sam963258

New Member
24 vote project ?

First let me say most logic circuits will not take 24 votes directly.
CMOS circuits were run from 5 to 15 volts.
TTL circuits are designed for 5 volts.
And the newer ICs are designed for even lower voltages.
Although there is a select few circuits that will take up to 30 votes or more on the output leads, these are specialty circuits and may be hard-to-find now and probably would not be suitable for your project.

I suggest using the following.

You will need a 5 volts DC regulated power supply as well as your 24 vote DC power supply.

For your time base I suggest a 555 timer.

This will trigger your flip-flop circuit and can be adjusted for the timeframe you need.

I also suggest you use optical couplings on the output side of the flip-flop to trigger SARs that will power 24 volts for your solenoids.
The optical couplings will prevent power surge from the solenoids from damaging the other circuits.

The SARs should handle the current needed to trigger the solenoids.

It also might help to put a 1 AMP 400 volt diode across the solenoid leads to give the current someplace to go when it is shut off.

A surge of 250 votes or more can be generated through a solenoid win the power is turned off. it will act like a automotive ignition coil. You wouldn't want your flip-flop being pounded with that much voltage.



I hope this helps
 

sam963258

New Member
PS

PS

I'm assuming this is going to be used outdoors in a wet area. Please observe all local electrical regulations in building a project. A GFI (ground fault interrupt) is recommended. Also the project itself should be inside protected from the weather.

Although I'm sure you probably know this and never hurts to be reminded.

Good luck.
 

goofy

New Member
Yes it helps because I have nothing to start with. Thank you.

I figured that I would have to use a couple of relays for the output voltage of 24vdc, but I thought that I could use the 24vdc as an imput voltage also just stepping it down to the needed circuit voltage. Am I not correct or are two power supplies definately needed?

I am attaching a tiny pic on the circuit I have so far. It's crude but it should show you guys where I am now.

Thanks for the help.
 

Attachments

sam963258

New Member
Relays were work fine just remember you can get the same rebounding voltage from a relay as you would a solenoid, approximately 250 votes.

If you cannot use separate power supplies stepping down the power supply from 24 volts 5 votes will work, just remember the higher the voltage difference the more heat that will be created within the regulator itself. you'll probably need a heat sink on the regulator.

I hope this helps
 

ljcox

Well-Known Member
Here is an option for you. The 555 will need an electrolytic capacitor. This one does not.

See attachment.

I don't see the need for optical isolation as suggested by sam963258.

My recollection is that the watering system solenoids draw a current of about 250 mA.

Len
 

Attachments

sam963258

New Member
your timer circuitry should work fine but he wants the outputs to alternate. When one is on the other is off. You'll need to invert the signal to one transistor.
also he'll have to order that circuit radio shack does not carry it anymore, at least not where I live.
 

goofy

New Member
Wow. Thank you. And I think I almost understand it completely, almost.

You said select C1 on test to trim the timing. I am not exactly sure what that means to be honest. I thought the 1M VR up top is adjusting the timing.

Also, the transformer I plan to be using is a max of 750ma, and it's designed to operate multiple solenoids. I looked at the ones I have and without the box I cannot tell.

Thank you for your help.

Alan
 

ljcox

Well-Known Member
Alan,
You're welcome.

The reason I said to alter C1 (if necessary) to trim the timing is because I did not do a precise calculation of the capacitor value nor did I consider the Schmitt Trigger threshold tolerances. CMOS Schmitt Triggers have relatively wide threshold tolerances. So you may find the minimum delay (ie. the delay with the pot set to its minimum resistance) is not 1 second as you require.

The pot is to allow adjustment from 1 to 60 second as you asked. It is not meant to be a trimming device.

As I said earlier, the solenoids in my watering system require 250 mA at 24 Volt (I don't now recall whether it is AC or DC). So if your transformer can deliver 750 mA max. then you can only have 3 solenoids on at one time. My watering system only ever has 2 solenoids on at a time.

Len
 

goofy

New Member
Cool. TY. I understand now.

I appreciate your help and I plan on building this circuit without a doubt. I do not understand a few of the valued components, but that is to my lack of knowledge. Once I find a supplier for the 4060, and I figure out what all the other components are, I can start construction. I took drafting and chorus in school, hindsight makes me wish I took electronics instead. :)

Once again TY all for your input and help.

Alan
 
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