How to make a DC motor timer?

Discussion in 'The Projects Forum' started by JPK777, Jul 27, 2009.

  1. JPK777

    Thread Starter New Member

    Jul 27, 2009
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    I made a battery operated fan to run inside my cigar humidor to circulate the air and maintain the humidity level. I am using a 1.5v dc motor with one D cell battery and a 10 Ohm resistor on the positive lead to slow it down a bit. I thought the resistor would help conserve the battery since it runs constantly. I'm not sure if this will help since I've read that resistors just drain energy in the form of heat. To remedy this, I would like to make a timer circuit that will run the motor (without the resistor) for 5 minutes on and 15 minutes off. I would really appreciate any help in the making of this circuit. I have a Radio Shack nearby, and that's what I have to work with for now. Thank you in advance for your help. I threw in a few pictures to give you an idea of what I'm doing.

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    Last edited: Jul 27, 2009
  2. Wendy

    Moderator

    Mar 24, 2008
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    The basic CMOS 555 timer should be able to do it, how into electronics are you (how much help do you really need)? You may need to up the voltage to 3V though, but there are some techniques that will still allow you to slow the motor (PWM) and conserve power.

    Just a suggestion, use the A/A button on the corner, and put each picture on it's own line. Having the thread extra wide is very distracting, and can make it a bit harder to post a reply.
     
  3. JPK777

    Thread Starter New Member

    Jul 27, 2009
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    The only electronics I've ever really played with was modifying my CB radios. I have worked with caps, resistors, and can solder on a board. I can't read schematics. Size is an issue with this project as well. Should I try using four AA batteries instead? Please point me in the right direction. I did read up on the 555 chip a bit, but did not find anything for my application on the internet. Thanks for the heads up on posting pictures too.
     
  4. sissow2

    Member

    Jul 14, 2009
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    You should have. The 555 is a timer circuit. If you hook up the appropriate resistor/caps, you can get the output of the IC to do what you want (up 5, down 15).

    You can then drive the motor from that output, either directly or through a power transistor (depending on the current draw, which im guessing is pretty low)
     
  5. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    You can do this pretty simple using a 555 but you need 3v.. search for 555 in astable mode and add a transistor at pin 3 to drive the motor.. Or if you go a bit deep, there are a few tricks with just relays..

    Just a suggession.. Try adding rechargable batteries to this..
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Actually the minimum voltage for a CMOS 555 is 2V, a regular 555 is 4.5V. I'd go with the CMOS myself, and either qty 2 "AA" or "C" cells. You might even manage to use that single D cell, but I'd advise against.

    To acquaint yourself with something like this I have some project drawn up, but to be able to help you you're going to have to learn some electronics, to the extent of reading a schematic. This may be too advanced.

    Check them out, and see if something like this is the route you want to go...

    The 555 Projects

    I'll help you design something that is a bit more efficient than what you have, but you'll have do to the hard part (for me this part isn't hard). :)

    You could also use a simple 2 transistor astable long duration multivibrator. Not as fancy, but you get to keep your existing battery and is much simplier to make. The life extending bells and whisltles aren't there, and it will show in battery life.

    BTW, I'll just add on to what you already have, you won't have to get rid of much. If I thought you could fit another D cell in there I'd go that route.

    Just asking, how long does your current set up last before you have to replace a battery?
     
    Last edited: Jul 27, 2009
  7. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    even a cmos 555 will waste some battery power in the external timing parts . perhaps using a small photo-voltaic for daytime use and a rechargeable battery for night use will minimize battery changes.

    i do not recall the chip #, but i though i saw a chip that is like a 555 but sleeps during the "off" time thus utilizing small uA during sleep time conserving power. does this ring a bell with anyone?
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    The trick with the 555 is use high values for the resistors, which will have to be done anyhow due to the long timing issue. I wouldn't worry about a couple of µa in this case.
     
  9. JPK777

    Thread Starter New Member

    Jul 27, 2009
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    I don't know how long my current set up lasts. I just made it yesterday. I like all the 555 projects you posted. I would like to make the CMOS chip set up. I just need a parts list and your suggestion on batteries. Four AA would fit just fine in the project box I have now. Thanks for all the replies.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Take a look the thread by dalder last page[8?]. Leave out the counter, re adjust timing resistors and you have almost what you want. Most of the small motors tried drew 70mA to 120mA.Note that the logic section runs on 3V @ about 100μA.If your motor is around 100mA , could also eliminate the BS170.The FTZ955TA, PNP low C-E sat. V, good gain, also surface mount.
     
  11. JPK777

    Thread Starter New Member

    Jul 27, 2009
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    Thanks. I'll have my friend help me read the schematic.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Have you measured motor running with prop current yet? What is the distance from top of D cell to inside of cover, logic board would be around 1/2 in.thick. Might be other solution to large timing cap [ 1000μF & 200μF ] I'm contiplating using a 4060 , 14 stage binary counter with oscillaror or for yours maybe a 4017 &C555.I'll be gone for about two days, but I'll keep trying to think.
     
  13. JPK777

    Thread Starter New Member

    Jul 27, 2009
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    I don't have much room, in fact I want to make it smaller if possible. I was thinking about maybe using a 9v with the current motor and experimenting with different resistors and just have it run constant and forget about the timer. Do you think that will work? Also, I have the switch wired through the ground. Should I have it wired through the positive lead? I ask this because I am not sure if the resistor constantly hooked up to the positive lead will drain the battery? Sorry about the simplicity of my questions. I am not very familiar with this.
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If it runs well on 1.5 then stay there with timer, it'll last many times longer on a D than on a 9V. If the D was moved to the side[if possible] ,how much space would be available? An AAA or AAAA cell would be used in series with D for timer for logic, good for hundreds of hours., excluding D.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    I like the two "AA" and "D" cell approach. Except I would use the 555 by itself and just make the timer do all the work, along with the transistor.

    Before I draw this up, do you want a speed control? It is the PWM project I've started, but not finished (the article, that is). They have dual 555 chips (called a 556), where it has two 555's in one package. I could merge two functions, a timer and a speed control, and it would be quite small.

    Normally I would have drawn this up already, but my work has gotten strange, and I'm working 7 days a week, and have other commitments besides. I will get around to it though.

    Just a suggestion. Put the fan and motor outside the box, and see how long that battery will last. This will give you a benchmarch to see how much improvement the circuit is giving.
     
  16. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    yeah, i'd use the 555 and a high gain darlington igbt to switch the motor on/off. you may run into a linear heating problem with a fet because the voltage available on the gate is very low so Rds(on) will not be attractive.

    this solution = simple.
     
  17. JPK777

    Thread Starter New Member

    Jul 27, 2009
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    I look forward to seeing this Bill. I would like to be able to control the speed as well. Thank you for all your help.
     
    Last edited: Jul 29, 2009
  18. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    JUst a quick report on 4060-74HC00; working great, timing 220kΩ & .2μF for timing. Can source 30 mA to drive PNP transistor. Using a FZT955TA drove a 100mA, 1.5V motor. Will draw it up when I get back from Mexico on Sat.
     
  19. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    This is running on a bread board with a" C" & a 2 " AAA's". The drain on the AAA's is 10μA , C drain depends on motor. OK to series C [ or a D ] with small battery like a N, AAAA AAA and add filter cap to +3V line.
     
  20. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    any flyback to worry about??
     
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