Constructing a "Power on time delay relay" with 5 sec. delay. max 6V
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Posted by on July 10, 2005, 10:43 am
Please log in for more thread options I'm trying to build an autonomous "sumo"-robot for competition in sumo-robot contests. One of the rules state that the robot must be inactive for 5 sec from the time it is switched on. Now I know that it probably would be much easier to buy a basic-stamp processosor and program it, but my budget is quite thin and I think it would be quite fun to construct a robot without software. I have found a circuit-drawing of a time delay relay, but it demands 12V and has a delay of roughly 7 sec. http://ourworld.compuserve.com/homepages/Bill_Bowden/page2.htm#delay.gif Since my motors run on 6V I would like the relay to do that as well. QUESTIONS: 1. How do I calculate the time delay? In the text the author states that the delay can be reduced by reducing the R or C values (R=47K, C=100uF)but is there a formula that can be used? 2. Will this solution turn the robot on at "full power" after the delay or will it start softly (when I push the button or when the time is up?)? 3. How do I have to change the circuit to reduce the voltage to 6V? 4. Is there a better alternative that wouldnt cost me more than perhaps 20$? As you can see I have'nt got much experience of electronics, so pelase be patient with me :) | |||||||||||||
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Posted by John Fields on July 10, 2005, 6:43 pm
Please log in for more thread options On 10 Jul 2005 07:43:56 -0700, david_gillberg@spray.se wrote: --- See below. --- >As you can see I have'nt got much experience of electronics, so pelase
>be patient with me :) --- Try this: (View in a non-proportional font like Courier.) +6V>---> |
S1 |
O | +-----------------------+------+ | | | | | | | | | +-------+-------+ | | | | | +-------+ | | +---+---+ [1M] |K | O COM | |_ _| | [DIODE] [COIL]- -| +--O|R D|O--+ | | O--> |<--O--->6VOUT
| |_ | | +-------+ NO NC
+--O|T TH|---+ | | | | C | OUT|---|--[100R]-----B +-------+ |+ E 7555 [4.7µF] | | | GND--------------+---------------+ _____ _______ When you close S1, the 7555 will come out of RESET before the TRIGGER input goes high, initiating an output pulse which will energize the relay for about five seconds. This will pull the common terminal away from the normally closed contact, disconnecting it from the switched 6V coming from S1. After about five seconds the 7555 will time out, de-energizing the relay, and 6V will appear on the normally closed contact. The nice part about this circuit is that the battery only has to supply current to the relay for five seconds, but the maybe bad part is that S1 has to be able to supply all the current needed by the 6V load. Will that work for you, or would you like something else? -- John Fields Professional Circuit Designer | |||||||||||||
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Posted by on July 10, 2005, 6:22 pm
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That sounds great. If I have understood it correctly that is ;). Correct me if I=B4m wrong: When power is switched on the the current will flow through the 7555 (and therefore through the base of the transistor) and the coil. The coil will act as an electromagnet "shutting of" the rest of the circuitry by pulling away the common terminal (COM?). When the 7555 times out power will stop flowing through the coil and start flowing through the rest of the circuit! Sounds like just the thing ive been looking for. A couple of questions arise: 1=2E How do i set the 7555 to time out after 5 sec? 2=2E The closest thing i found att my components shop is something they call "ICM 7555" would that be what your thinking of? (do you know what ICM stands for?) 3=2E What is the diode doing in the circuit? 4=2E Is the "[4.7=B5F]" a capacitator? 5=2E What does NO and NC to the right of the circuit stand for? Phew, I think I=B4m running out of questions for the moment ;). Thanks a lot (and again for your patience, if this project works I sure will have learned a lot from it :). /David | |||||||||||||
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Posted by on July 11, 2005, 4:48 am
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OK, I found out what NO and NC stands for (Normally Open and Normally Closed), but then another question arose... Can a relay be both NO and NC? Do you buy a specific NO or NC relay or is it just a question of how you turn it when hooking it up to the rest of the circuit? /David | |||||||||||||
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Posted by Randy Day on July 11, 2005, 11:51 am
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david_gillberg@spray.se wrote: > OK, I found out what NO and NC stands for (Normally Open and Normally
> Closed), but then another question arose... Can a relay be both NO and > NC? Yes. Look for a DPDT (double pole, double throw) relay. That way you'll have two sets of contacts which can be used either as NO or NC. Assume the relay below is at rest (not powered). Contacts a and c are NC, e and f are NO. o- b a -o--__ | o- c | | | | o- f e -o--__ o- g (created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de) > Do you buy a specific NO or NC relay or is it just a question of how
> you turn it when hooking it up to the rest of the circuit? You can buy SPDT, DPDT, 4PDT, etc. relays. It's in how you hook them up... HTH | |||||||||||||
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>sumo-robot contests.
>One of the rules state that the robot must be inactive for 5 sec from
>the time it is switched on. Now I know that it probably would be much
>easier to buy a basic-stamp processosor and program it, but my budget
>is quite thin and I think it would be quite fun to construct a robot
>without software.
>
>I have found a circuit-drawing of a time delay relay, but it demands
>12V and has a delay of roughly 7 sec.
>
>http://ourworld.compuserve.com/homepages/Bill_Bowden/page2.htm#delay.gif
>
>Since my motors run on 6V I would like the relay to do that as well.
>
>QUESTIONS:
>1. How do I calculate the time delay? In the text the author states
>that the delay can be reduced by reducing the R or C values (R=47K,
>C=100uF)but is there a formula that can be used?
>
>2. Will this solution turn the robot on at "full power" after the delay
>or will it start softly (when I push the button or when the time is
>up?)?
>
>3. How do I have to change the circuit to reduce the voltage to 6V?
>
>4. Is there a better alternative that wouldnt cost me more than perhaps
>20$?