# NEED: Long-term Timer Circuit Diagram

#### charlessenf

Joined May 24, 2005
12
I want to lock my dog in his pen until I get out of the driveway so he won't chase my car.

I was thinking a retracting solenoid could be used to hold the (spring-loaded) door shut until it was activated, whence the dog to the cage would "spring" open and he could roam about at will.

It appears that I need a timing circuit such that I could energize it with the push of a button, then leave. When the set time (30 minutes would be max - 15 Min would be OK) had expired, I would need the circuit to close a relay so I could energize the PULL solenoid to release the latch and open the cage door, then shut itself (the circuit) off. No use using power once the door's open and the dog is gone.

I've found a Long Term Timer in one of my books [Rudolf Graf Electronic Circuits V2], but it requires manual switching to power things down. And was not detailed enough for me to follow - assumed [I had an] E.E. Degree I think.

I'm not the E.E. some of you are and would need sources/circuits with sufficient explanations attached so I would know which capacitor value or resistor value to vary to control the time, etc.

I have the MECHANICS down. I just need a way to time and power the solenoid.

6VDC would be GREAT (4 "D" Cells) as I would like the entire affair to fit on the cage in a small container that I could remove as necessary and not need to wire to the mains. But, I could live with a Wall Wart powered setup easily enough and have some 12vdc-13VDC Wal-Warts on hand.

Charles

#### Wendy

Joined Mar 24, 2008
22,328
Define long term timer, how long before it triggers, and long does it stay on after it triggered.

#### charlessenf

Joined May 24, 2005
12
Define long term timer,
how long before it triggers, and
9HOW0 long does it stay on after it triggered.
1. 15-30 Minutes
2. Just long enough for the solenoid to retract - <1 Sec?

I could rig it so that the solenoid, as it retracts (PULLS) the latch open, it opens an N.C. Momentary switch to shut down the circuit.

I was assuming that the timer circuit would be enabled (the timing cycle started by pushing a N.O. Momentary Contact switch. That, when the set time had been reached, the solenoid circuit would be powered momentarily; the solenoid would be pulled in (which would release the mechanical latch, thus allowing the cage door to "spring" open and release the dog.) I assumed such a circuit would "go to sleep," then, requiring no power consumption) until the next time the "start" switch was pressed.

Of course, I wouldn't be asking for help if I was certain this could be accomplished with a small electronic circuit.

Thank you for the response. Happy New Year. Charles

#### Wendy

Joined Mar 24, 2008
22,328
How good with software are you? Reason I ask is there is a class of circuits called µC that people will recommend.

Over all they require fewer parts, and if you have the equipment to program them take a lot less parts.

The other option is pure hardware. Something using a CD4060 and a 555 integrated chip.

#### tracecom

Joined Apr 16, 2010
3,944
@Bill,

Would a standard 555 monostable circuit work? With a 1M/1000μF R1/C1 combo, the output would stay high for about 18 minutes, which is within the OP's window. The output would hold the solenoid energized, which would be configured to keep the gate locked. In addition, the output could hold a relay operated with a set of NO contacts through which the power to the 555 was routed.

In operation, there would be a momentary start switch, which when operated, would provide power to the 555, the output of which would operate the solenoid to lock the gate and would also energize the relay, which would continue power to the circuit. When the 18 minutes was up, the output from the 555 would go low, releasing the solenoid and the relay. The dog leaves and the circuit draws no power.

ETA: It probably would make more sense for the 555 to just operate a relay and route the power for the solenoid through the relay.

#### Wendy

Joined Mar 24, 2008
22,328
15 - 30 is doable, but then he will need a second timer for the solenoid. If I can replace one the chips with a 4060 it should be a bit smaller. One thing for certain, the solenoid is going to spike the power buss.

#### tracecom

Joined Apr 16, 2010
3,944
15 - 30 is doable, but then he will need a second timer for the solenoid. If I can replace one the chips with a 4060 it should be a bit smaller. One thing for certain, the solenoid is going to spike the power buss.
The circuit below is what I had in mind. Please point out any problems.

The idea is that until the button is pushed, there is no power on anything, and therefore no battery drain. When the momentary NO button is pushed, the 555 goes high, which operates the relay. The relay feeds +V to the 555 and to the solenoid until the 555 times out. At that time, pin 3 goes low, the relay drops, the solenoid drops, the dog pen gate latch is open, and there is no further battery drain.

Using separate contact sets for the 555 power and the solenoid should avoid problems when the solenoid drops.

I think I have D1 pointed the right way, but check it.

With the R1/C1 as shown, the 555 should stay high for about 1100 seconds (18.33 minutes.)

I am not sure of the value for R3.

I have breadboarded the circuit except for the solenoid. It seems to work.

What do you think?

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#### Wendy

Joined Mar 24, 2008
22,328
OK, I see how the relay powers the circuit while the 555 is timing, but it is also power the solenoids. You want to power the solenoid after the 555 times out, for a very short duration. This is why I suggested a second 555 circuit, for this short pulse on the solenoid.

Relays are power hogs, the duration it is one probably exceeds the total power used by something like a CMOS circuit every day by quite a bit. This could be swamped by the power used by a solenoid, but in general it is best not to use a relay for battery applications.

I'll draw something up that does not use a relay. You will probably need a really large capacitor for the power supply, the batteries will only power a solenoid while they are fresh. A large capacitor will provide the majority of the current while the solenoid is on, or at least that is the hope.

I have some drawing to do on a schematic, I'll be back after I'm done to post them.

#### Wendy

Joined Mar 24, 2008
22,328

Q1 is a specialized part called a logic level MOSFET. Something like a RFD16N05L would work. Mouser Electronics carries these parts.

C8 needs to be as large as you can make it. The value named is for convenience.

CR1 and CR2 should be large current Schottky diodes. You can try regular diodes such as 1N4001, but CR2 probably needs to be fast. CR1 is extremely none critical. I recommended the Schottky because they will improve operation overall.

I have no clue what solenoid you are planning on using. The battery voltage is somewhat dependent on that. The transistor is rated for 16A, so it should be good.

The timers are a specialized version of the 555 called CMOS 555s. You must use CMOS parts here, else your battery will run down very very quickly. A 7555 is a version of a CMOS 555, Radio Shack sells a version called a TLC555.

You can replace these two chips with a dual CMOS 555, such as a 7556.

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#### thatoneguy

Joined Feb 19, 2009
6,359
How good with software are you? Reason I ask is there is a class of circuits called µC that people will recommend.

He doesn't seem to desire a long term relationship with electronics, so the $50 startup cost would be too much when a counter circuit could be used. I'd also suggest something like the 4060 with oscillator, then use the desired set of outputs for switch and sleep. #### Wendy Joined Mar 24, 2008 22,328 I thought about it, and even have schematics I could modify that are very close to that. It was 5 of one and 5 of the other. I went with a simpler circuit. Look at his profile, he is a very unusual user. I suspect he may not be back, though I have hopes. Thread Starter #### charlessenf Joined May 24, 2005 12 ... else your battery will run down very very quickly. A 7555 is a version of a CMOS 555, Radio Shack sells a version called a TLC555. I figured out how to address the power down issue. Power is only supplied to the circuit while the gate is in the close position. Once the solenoid pulls and releases the latch, the micro-switch (trip) attached to the gate will allow the MS (in series with the battery(ies) to open shutting off the power. How's that? And, I am open to a relatively short learning curve and low-cost digital approach. I looked at PICAXE site, but there were so many options to choose from - make that "too many." No site for old men (;harles Thread Starter #### charlessenf Joined May 24, 2005 12 I;m Baaaaacccck! How good with software are you? ... class of circuits called µC that people will recommend. Well, I cut my teeth programming the Sinclair, TI-9/4a, Apple IIe, Tandy Model III, taught FORTRAN, COBOL, B.A.S.I.C. many years ago. No Machine Language programming experience at all. See my comments, please, re: PICAXE. It would appear that, using something like a PICAXE and controlling the power to the circuit with the gate latch (same post) idea, that I could have/get a circuit that could devote most of the limited power to the Solenoid for that essential moment without draining the batteries so much/fast as to render the effort more expensive (in battery replacements) than it's worth. From what I gathered so far, it would seem that there might be a "stater kit" available that, with some help here, could be put to use if my Windows Vista laptop could be employed to write and d/l the instruction set to the circuit and the chip could "remember" the instruction set after losing all power (when the gate opens). This would enable programming a standard time and (with the power on when gate is closed approach) eliminate the need for a separate "START" switch. Although an LED to indicate it was "working" would be nice if it did not consume an inordinate amount of power, of course. I was hoping to avoid the need for a relay as that would require another coil which (as I understand things) puts more demands upon the limited power source. I had hoped for a solid state solution that would actuate the Pull Solenoid that would release the latch and disconnect the power to the circuit. Later, I could add a circuit that would use the open gate event to connect the (now, re-chargeable) D cells to a charging circuit (If I could find one that could be left on 24/7 w/o damaging the batteries or the components of the charging circuit - I've had several of the Harbor Freight Tools ($2,99 ) 12VDC trickle chargers melt their diodes on me when left on for days.

To my untrained eye, http://forum.allaboutcircuits.com/attachment.php?attachmentid=38356&stc=1&d=1325429784, looks to be the simplest implementation if we could eliminate the relay and replace it with the solenoid. Of course, I have no idea how to do that off hand.

Thank you again. (;harles

#### Bernard

Joined Aug 7, 2008
5,773
If you look at your preffered ckt, pg. 13, you will see that it does not meet your requirements. At turn on, trigger, pin 2 is held low, setting output high for duration of timing cycle, approx. 1000 sec, also energises latching relay & solenoid- opening door at start. The two C555's draws little current when off- maybe 100 μA- good for around 5,000 hours with D's, or 1000 hours with AA Ni-Cd's; which would only require a small solar panel to keep charged.

#### tracecom

Joined Apr 16, 2010
3,944
I have done some looking for a suitable solenoid and have not found a single one that runs on 6 volts. With that in mind, and considering that you will have to fabricate the latch mechanism, I suggest that you look for a solenoid that you can develop the mechanics around. That will dictate the voltage and current required. Based on your previous comments, I am sure that you will look for a solenoid with the lowest power requirements necessary to do the job. Of course, it will still have to have the power that your latch mechanism dictates. Once you have identified a solenoid, an electronic design (555, PICAXE, or whatever) will be relatively straigtforward.

The "simplest implementation" that you pointed to is my suggestion. It does have a significant drawback in that the relay and the solenoid are both under power during the entire time the gate is latched. However, at all other times, the circuit draws no power whatsoever.

A MOSFET can be substituted for the relay in my suggestion, and may be a significant improvement, however, I believe that the current draw of the relay will be insignificant when compared to the solenoid.

To reiterate, I think the first logical step is for you to select a solenoid. That will tell us the voltage and current that we must deal with, and therefore whether it is feasible to run it on batteries. In addition, it will ensure that the solenoid selected is something that you can incorporate into a functional mechanical design. It might even be worthwhile for you to test the solenoid in your design to be sure that it has the power necessary to control the latch.

ETA: I was writing this while Bernard was posting.

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#### tracecom

Joined Apr 16, 2010
3,944
If you look at your preffered ckt, pg. 13, you will see that it does not meet your requirements. At turn on, trigger, pin 2 is held low, setting output high for duration of timing cycle, approx. 1000 sec, also energises latching relay & solenoid- opening door at start. The two C555's draws little current when off- maybe 100 μA- good for around 5,000 hours with D's, or 1000 hours with AA Ni-Cd's; which would only require a small solar panel to keep charged.
You are correct about the power drain while the circuit in post 7 is under power, and that may make the circuit undesirable. However, whether the solenoid latches the gate or releases the gate when under power is a matter of mechanical design. I had visualized a push solenoid that extended a locking pin through a hole in the gate frame to keep it locked during the 18 minute period. But there are other ways to design it, some of which may have a better mechanical advantage.

#### charlessenf

Joined May 24, 2005
12
"I had visualized a push solenoid that extended a locking pin through a hole in the gate frame to keep it locked "

OP here. Mechanically, that was what I had in mind except that, in my conception, the closing of the door engaged the extended solenoid "bolt" which, in turn, held the door in the closed position UNTIL energized/retracted, thus releasing it's "hold" on the door which, then would spring open releasing Jackson. Absolutely no power required to keep the door closed.

The timing circuit power source (batteries) would also be switched on when the door is closed, off when the door is opened.

So, when you close the door, you provide power to the circuit, but the timing cycle does NOT begin until and unless you press the START button.

Then, when the time expired, power would be sent to the solenoid, retracting the "bolt," letting the door swing open and disconnecting the power to the circuit. After all, no one's going to need it until the next trip to the store so why not disconnect the batteries?

My apologies if my responses do not appear in the "right" places. Getting use to this board again after a number of years and I was confused, at first, by the comments directed to other than the OP. (;harles

PS: I will do a bit more research on the solenoid so I can offer the specs of the most efficient I can find that will work the latching mechanism in mind. The weather took a turn for the freezer (17 degrees) so the workshop is less inviting than ever. This weekend will be warmer and I''l get to it then.

#### tracecom

Joined Apr 16, 2010
3,944
PS: I will do a bit more research on the solenoid so I can offer the specs of the most efficient I can find that will work the latching mechanism in mind. The weather took a turn for the freezer (17 degrees) so the workshop is less inviting than ever. This weekend will be warmer and I''l get to it then.
I don't think you will find a suitable solenoid that will operate on less than 12V, but that's not really that big an issue. Eight D cells would do, or you might want to consider a 12V SLA battery with a solar charger. A 555 based circuit would run on 12V, but a microcontroller would require regulating the 12V down to about 5V, or you could run the μC from a separate set of batteries (e.g. 3 AA's.) The nice thing about a μC is that the timing would be programmable, and the solenoid could be pulsed (via a MOSFET) at whatever time interval you want.

#### charlessenf

Joined May 24, 2005
12
"and the solenoid could be pulsed (via a MOSFET) "

Oh, I love it when you talk techie to me. Of course, I don't have a clue as to what that means. My understanding is that the solenoid needs but one "pulse" to pull it open/back and release the door/gate.

Honestly, I do not understand the pulse thing.

#### thatoneguy

Joined Feb 19, 2009
6,359
Solenoids typically do not have much "throw", mabye 3/4" effective at best, and no holding power.

Something like a linear actuator may be more what you are looking for, so it can actually bar the door through the standard "hook loops" found on chain link fences, which would still allow you to open the gate by manually lifting the lever that latches over the bar.