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very simple time delay circuit

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I am looking for a simple delay circuit that will delay the start of 1.5 volt hobby motor... The time does not have to be exact every time,, I am looking for a delay of between 5 and 20 minutes. Is it possible to do this without a 555 and a relay?

Ant suggestions would be greatly appreciated.


thanks
 

Sceadwian

Banned
5 and 20 minutes? That's a bit broad. 555's are generally more reliable under 10 minutes so you could use a 555. There are more than enough examples on the net on how to set a 555 up as delay timer.
 

MikeMl

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Most Helpful Member
Richard, any time delay of 30 minutes based on just an RC time constant gets problematic because the product of R and C must be 1800. If you use a 1Meg resistor, the capacitor has to be 1800/1000000=1800uF. The leakage of such a large capacitor exceeds the current that the timing resistor can supply (a few uA), which prevents the capacitor voltage charging to the triggering threshold. For example, this Panasonic 1800uF 15V electrolytic capacitor has a leakage current of 288uA.

A way to get this length of timing is to use a 14541B CMOS Oscillator/Timer chip. It only takes two resistors, one tiny capacitor along with this chip to produce a delay up to hours...
 
I am very sorry < I meant to say 5 to 20 SECONDS. Could I still do this with only a 14541b, 2 resistors and one capacitor?


thanks again,,,,sorry about the mistake.
 

MikeMl

Well-Known Member
Most Helpful Member
Data Sheet

You may have to add a FET to turn on the motor.
 

Hero999

Banned
I am looking for a simple delay circuit that will delay the start of 1.5 volt hobby motor... thanks
A 555 won't work because it requires 4.5V.

A 14541b won't work because it requires 3V.

A couple of transistors arranged as a monostable might work.

How much current does the motor require?
 
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KMoffett

Well-Known Member
Richard,
Is the 1.5v battery(?) the only power source available. Maybe you could explain a little more about the project. If higher voltages sources (batteries or wall warts) are an option, there are a myriad of usable timer circuits...including the 555.

Ken
 
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My project is a "streetcar" traveling down a track run by a d size battery. A nonc micro switch is on the side of the car and when it hits a raised bumper along the track which makes it stop. This turns off the main circuit and opens the time delay faze that simulates the streetcar stopping for passengers or a stoplight. I now have a very Heavy and complicated ICS delay device that is run by heavy 9 volt battery that delays for 20 seconds....I am looking for something simple, light weight that when the micro switch is tripped the car will be stopped for a time between 5 or 20 seconds...Is there a simple way? Even perhaps non electrical?
 

Boncuk

New Member
Hi Reinhard,

if you have enough space to accomodate two LR44 batteries you might use a CMOS device for timing.

Wire the output to a low power MosFet to obtain max speed for the motor. (1.5V)

Boncuk
 

KMoffett

Well-Known Member
Reinhard,

Do you have any idea, or a way of measuring, how much current the motor draws?

I have an idea for a circuit that will do what you want. It would mean adding set of small batteries to provide 6v at a low current.

ken
 

KMoffett

Well-Known Member
The circuit works...so far. But I still need to know the current draw of the motor.

Ken
 
Hi Ken'
This I cannot tell.I used an ometer and I think it showed 100 ohms...I really do not know howq to read one of those things. All I can tell you is that I use Nicad D size batteries, which really are only at 1.2 volts.....The car can run over an hour before expiring..
I hope this is helpful.
I am willing to try anything.


Thank you again

Richard Reichardt
 

Hero999

Banned
Here's a circuit that will work from a single AA cell.

how much current does the motor require?
 

Attachments

KMoffett

Well-Known Member
If he is using a D-cell NiCad that only lasts 1 hour, and the motor resistance is 100Ω, I wonder at what voltage the motor no longer runs.

Attached was my solution. Was trying to select Q2.

Another solution was just using a PICAXE-08M µC with 4 AAA's , detecting the switch and driving the MOSFET in my circuit, with µA current draw.

Ken
 

Attachments

Thank you everybody,,,,,,,Just one question,,,what type of a switching transistor would you recommend? I found a lightweight small 12 volt security battery. Now with 12 volts
can I make a much simpler circuit with ok, A relay,,one transistor , a couple of resistors and a capicitor.....perhaps a zener diode to stablize the load on the transistor.


thanks again
 

Frosty_47

New Member
Thank you everybody,,,,,,,Just one question,,,what type of a switching transistor would you recommend? I found a lightweight small 12 volt security battery. Now with 12 volts
can I make a much simpler circuit with ok, A relay,,one transistor , a couple of resistors and a capicitor.....perhaps a zener diode to stablize the load on the transistor.


thanks again
any N-channel EMOSFET with drain current of 3A or more will do the job well. There is no need for zener diode.
 
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Thunderchild

New Member
just use and RC circuit and a comparator, if it needs restating often put a much larger resistor in paralel with the condenser to help it discharge so its ready to go again else it will self discharge into the comparator when off andbe ready to go again later. just remember comparators do not supply current as the outputs are open collectors
 

KMoffett

Well-Known Member
I like Hero999's transistor monostable circuit, with high-side switching. But, since it has no values, I wonder how it will work for a 20-second period, and with less than 1.25v from Richard's nicad battery voltage.

With that design in mind, I modified my dual monostable to a single 555, moved the microswitch out of the motor circuit, and added a low Rds logic-level, P-channel, high-side MOSFET.

For a low current timer, I would still go with, three 1.5v button cells, a PICAXE 08M µC, one resistor (pull up), one diode (flyback), and a N-MOSFET.

Ken
 

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