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 Post subject: And now for someting completely different, almost
PostPosted: Jan Fri 26, 2007 5:56 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1450
Location: Watsonville, CA, US
Can anyone point me to a timer circut that will allow me to to turn a small 3V DC motor off and on at regular intervals? Maybe 2 seconds on and five off. I want to extend battery life by running it intermittantly. I have not done any significant solid state building and don't know where to start. It is for a homebrew antimated duck decoy I want to make. It will be my version of this:

http://www.wonderduck.com/

The achillies heel fo these kind of thing is that the batteries go flat. The mechanics of building it should be no problem. I have found the gear box I need to make the paddlels spin. It also seems intermittent splashing should look more natural.


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 Post subject:
PostPosted: Jan Fri 26, 2007 6:21 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 9107
Location: Santa Rosa, CA
Try an NE555 timer circuit. You'll find tons of ideas on the Internet. This little IC has been around for over 30 yrs, but is very versatile and will operate on 5V DC or more.

http://www.kpsec.freeuk.com/555timer.htm

There are all sorts of "cookbooks" showing timer circuits that will give seconds or even minutes as intervals.

If you are running a small DC motor, then you might power the 555 from a 9V radio battery and motor from D cells. The 555 will easily drive a power MOSFET that can turn the motor ON.

Good luck.

Rich


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 Post subject:
PostPosted: Jan Fri 26, 2007 6:47 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1450
Location: Watsonville, CA, US
Rich, W3HWJ wrote:
Try an NE555 timer circuit.

There are all sorts of "cookbooks" showing timer circuits that will give seconds or even minutes as intervals.


Rich


That link is a good start.

Can someone point me to a circut with values or a specific book I should get. I am but a simple caveman. I am more interesed in results than learning the thoery on this one.

Thanks.


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 Post subject:
PostPosted: Jan Fri 26, 2007 6:51 pm 
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Joined: May Tue 30, 2006 8:34 pm
Posts: 169
Location: Akershus, Norway
Well, I made a little timer for a friend, a year ago or so, to be used for a screw feeder i an old pellets stove. It works perfect to this day.
Image

If you want the PCB pattern, let me know.


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 Post subject:
PostPosted: Jan Fri 26, 2007 8:05 pm 
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Joined: Jan Tue 02, 2007 3:20 pm
Posts: 45
Location: Toms River, NJ USA
Love the duck idea, you may be able to trickle charge your battery during the day to extend battery life by scrounging the solar charging system from a walkway light. Harbour Freight has some on sale:
http://www.harborfreight.com/cpi/ctaf/d ... mber=90729
If I was a duck design engineer, I'd figure a way to counter weight the moving parts to minimize the load on the motor, may extend battery life further
There may still be some 30 in 1 (60 in 1 and etc.) electronics kits still floating around that may help you protoype a solid state ciruit before you solder things together.


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 Post subject:
PostPosted: Jan Fri 26, 2007 10:52 pm 
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Posts: 1450
Location: Watsonville, CA, US
Rune wrote:
Well, I made a little timer for a friend, a year ago or so, to be used for a screw feeder i an old pellets stove. It works perfect to this day.
Image

If you want the PCB pattern, let me know.


Will this circut give a few seconds on then a few off? I am thinking the pellet stove would be much slower. What compontents would I modify to get the intervals I am looking for? What would the approximate values be?


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 Post subject:
PostPosted: Jan Fri 26, 2007 11:15 pm 
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Location: Akershus, Norway
Scot Armstrong wrote:
Will this circut give a few seconds on then a few off?

Yes. "t2" gives you approx 0 to 7 secs. So if you change the value of C1, to that of C2, you will have equal time range on both timings.
Scot Armstrong wrote:
What compontents would I modify to get the intervals I am looking for?

You can change C1(or C2) to any suitable value, and/or P1+R2. Remember that P1+R2 should have no lesser restistance than 4.7k (<-R7) in total.


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 Post subject:
PostPosted: Jan Fri 26, 2007 11:31 pm 
To make it less "cryptic":
R2, R7......... 4.7k
C1, C2 ........ 0.01u

Rune


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 Post subject:
PostPosted: Jan Sat 27, 2007 3:21 am 
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Location: Livermore, CA
Scot

You can use IC's and the mentioned circuitry but for only a couple seconds cross coupled transistors will work.

Using 2 NPN transistors emitters to negative. Base of each to + through resistors selected for timing. Collector of one with a resistor to + the other motor to +. Be sure to add a diode across the motor. Kick back spikes from a motor tuning off will destroy semiconductors.

Also needed are 2 - 100 mf @ low voltage, between each base and the opposite collector. Base resistor & these caps control timing.

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Norm


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 Post subject:
PostPosted: Jan Sat 27, 2007 5:12 am 
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Location: Watsonville, CA, US
Norm Leal wrote:
Scot

You can use IC's and the mentioned circuitry but for only a couple seconds cross coupled transistors will work.

Using 2 NPN transistors emitters to negative. Base of each to + through resistors selected for timing. Collector of one with a resistor to + the other motor to +. Be sure to add a diode across the motor. Kick back spikes from a motor tuning off will destroy semiconductors.

Also needed are 2 - 100 mf @ low voltage, between each base and the opposite collector. Base resistor & these caps control timing.


That is nice and simple! So. 9V battery?, any guess on the resistor values? What diode and what orientation? No need for a relay?


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 Post subject:
PostPosted: Jan Sat 27, 2007 4:50 pm 
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Location: Livermore, CA
Scott

All depends on motor requirements? How much current does it draw? If you are able to use a 9 volt transistor radio battery probably not much. If the motor draws a lot of current might have to add a driver transistor but a relay won't be needed.

Put the diode across your motor with cathode (stripe) toward positive.

I would start with 1K in the collector without your motor. 10K for base resistors to B+. These can be adjusted to control timing. 10K and 100 mf give a time constant of 1 sec. Overall these values might give 1 sec on and one off.. Adjust by adding capacity for longer time constant.

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 Post subject:
PostPosted: Jan Sun 28, 2007 12:00 am 
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Posts: 1450
Location: Watsonville, CA, US
Norm Leal wrote:
Scott

All depends on motor requirements? How much current does it draw? If you are able to use a 9 volt transistor radio battery probably not much. If the motor draws a lot of current might have to add a driver transistor but a relay won't be needed.

Put the diode across your motor with cathode (stripe) toward positive.

I would start with 1K in the collector without your motor. 10K for base resistors to B+. These can be adjusted to control timing. 10K and 100 mf give a time constant of 1 sec. Overall these values might give 1 sec on and one off.. Adjust by adding capacity for longer time constant.



We are getting very close. I was thinking of running the timer off a 9V battery and the motor off a couple of D-cells. The relay was to accomidate that. Are you suggesting I run the whole works off the D-cells and keep it all one circut?


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 Post subject:
PostPosted: Jan Sun 28, 2007 3:18 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Watsonville, CA, US
Here is what I made. It does not work. Anyone know why?

http://antiqueradios.com/gallery/view_p ... ent&id=NPN


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 Post subject:
PostPosted: Jan Sun 28, 2007 3:47 am 
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Location: Powder Springs,Ga. USA
You need to cross couple the capacitors as shown in the schematic for the astable multivibrator here.

http://en.wikipedia.org/wiki/Multivibrator#Astable_Multivibrator_circuit

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Terry, K4TLJ
"Never run out of airspeed, altitude and ideas at the same time"


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 Post subject:
PostPosted: Jan Sun 28, 2007 4:05 am 
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Location: Saskatoon
Terry beat me to it, but this is what I drew:

Image


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 Post subject:
PostPosted: Jan Mon 29, 2007 12:42 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1450
Location: Watsonville, CA, US
Terry Judkins wrote:
You need to cross couple the capacitors as shown in the schematic for the astable multivibrator here.

http://en.wikipedia.org/wiki/Multivibrator#Astable_Multivibrator_circuit


The first on on that page works and the time period is good. The DVM cycles up and down nicely. :D Problem is it won't run the motor. :( It just stays at zero with the motor connected. I am guessing that the short from the brushes is the snag. Might I be able to use a small relay? Would the coil in it cause the same problem? How about a driver transistor? What does that look like?


Last edited by Scot Armstrong on Jan Mon 29, 2007 1:28 am, edited 1 time in total.

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 Post subject:
PostPosted: Jan Mon 29, 2007 12:55 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Livermore, CA
Scot

How much current does the motor require to operate? You can add a transistor driver. A relay wouldn't be necessary.

One other thing. I would reduce those resistor values by a factor of 10 and increase cross coupling caps by the same factor, 100 mf. This will give 10 times the drive current. Available motor current depends on transistor gain. With 150K base resistor you will only have a ma or so for collector drive.

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 Post subject:
PostPosted: Jan Mon 29, 2007 1:35 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1450
Location: Watsonville, CA, US
Norm Leal wrote:
Scot

How much current does the motor require to operate? You can add a transistor driver. A relay wouldn't be necessary.

One other thing. I would reduce those resistor values by a factor of 10 and increase cross coupling caps by the same factor, 100 mf. This will give 10 times the drive current. Available motor current depends on transistor gain. With 150K base resistor you will only have a ma or so for collector drive.


Hello Norm,

Thanks so much for the help, again.

It is a little DC motor that you used to be able to get at RAT Shack. Big around as a nickel and about an inch long. It runs great on 3V. I have no idea of the current. If I swap values would I be likely to run the motor to full strength?

Rather than tearing it apart again could a driver transistor be added? I have pleanty of room on my little perf board.


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