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DELETED (Inactive)
4 Posts |
 Posted - Jun 17 2004 : 12:50:12 PM
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I have an older model Harley motorcyle without self canceling turn signals and it's awkward to keep the buttons pressed while operating the clutch, brake, throttle. It looks like the "Time delay relay" in Aaron's circuits section would do what I need. Some questions: -
1.- I assume I'll need seperate circuits for right and left signals?
2.- Is there a time factor for the actuating switch ? ie: does it have to be pressed until capacitor is fully charged ? What happens if you keep the button pressed?
3.- Aarons schematic shows the 555IC pins out of real location. This was done to simplify the schematic?
I totally rewired the bike, but I'm pretty weak in electronics, so please be gentle and thanks in advance for any help you may give.
John
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DELETED (Inactive)
56 Posts |
Posted - Jun 17 2004 : 3:21:51 PM
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1. Probably, depending on how the switch is wired.
2. There should not be. The capacitor is actually charged in it's "unpressed" state, pressing the switch allows the capacitor to discharge (If I'm reading the schematic correctly.) during which time, the relay will be active. This circuit is called a monostable multivibrator if you want to look up more stuff about it on the net. There are also a good number of other schematics readily available using inexpensive parts to experiment with. Holding down the switch would have little or no effect on the function of the circuit, as the timer will reset once the cap has discharged. There will then be a "recharge" time before the circuit can be activated again. The circuit could be modified to activate the relay while the switch was down, and trigger the delay after the switch goes back up if you want to leave the signal on for an extended time.
3. It's common to do that on schematics, as it's really a logic diagram, and not a physical representation. Often the sides of an IC are separated into + power, -power, input and output as it helps identify the logical functions of the IC. Some times it's just a neatness thing, and sometimes since we tend to just use a drawing package for schematics, it was organised for one circuit to make it all nice and neat, and we're jus using the same drawing of the component over again, so it's a mess for no readily aparent reason. :)
(edit for spelling)
Edited by - SupraGuy on Jun 17 2004 3:25:15 PM |
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DELETED (Inactive)
56 Posts |
Posted - Jun 17 2004 : 4:04:51 PM
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One more thing...
It occurs to me that the use of a schmitt trigger in conjunction with a capacitor, diode and resistor may be more to the purpose of what you want.
A schmitt trigger is basically a circuit that remains ON as long as an input voltage is above it's trigger value This would require that you hold the buton down long enough to charge the capacitor, however, using the diode to bypass the resistor for charging would make this time minimal. When you release the button, the capacitor would discharge through the resistor, leaving the voltage high for the trigger for a time. This has the benefit of not flashing your signal light for 20 seconds if you accidentally hit the button, and gives you the option of having the signals on for a longer period by holding down the button, which the monostable (Also called one-shot, by the way) does not.
I'd need to do some experimentation to get component values for this kind of trigger.
A tentative parts list would be (Per circuit)
2 NPN transistors similar to 2n222
1 timing capacitor (47uF?)
1 timing resistor (100k ohm?)
1 bypass diode
2 3.3k resistors
2 2.2k resistors
1 10k resistor
1 1k resistor
plus the relay and bypass diode for the relay.
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DELETED (Inactive)
4 Posts |
Posted - Jun 17 2004 : 8:32:07 PM
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Thanks much for your help SupraGuy. I've already ordered the parts for the 555 relay and I'm looking forward to experimenting. The diagram shows a 1meg pot for timing adjustment (0 to 20 seconds) and I'm shooting for about 7 to 10 seconds. If I need more I'll just press the button again. If that works out OK, I'll just replace the pot with an appropriate resistor. Schmitt's trigger sounds interesting too. I'll check it out.
Thanks again
John
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DELETED (Inactive)
4 Posts |
Posted - Jun 24 2004 : 9:04:27 PM
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Hey SupraGuy, are you out there? I built a time delay circuit prototype and it worked fine for about 12 cycles and then it locked up closed. I replaced the 555 IC and it started working again for another 12 or so cycles and locked up again. If I crank the pot to less resistance, the relay will release, but the circuit wont work again unless I replace the IC. Any ideas? Thanks.
John |
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DELETED (Inactive)
56 Posts |
Posted - Jun 24 2004 : 11:19:33 PM
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Sounds like you're frying the IC somehow. Most of the circuits that use a 555 timer run on 9V or less, so perhaps using an LM7809 voltage regulator on the power for the IC would be a good idea, or possibly even a lower voltage. Of course you'll have to change the relay that you're using in order to use the lower voltage...
Also, it's a good idea to put a diode across the relay activation terminals to prevent reverse voltage spikes back to the IC. If you don't have that in place, it's the first place to start.
I'd like to see a schematic of your finished product, it would help in seeing what may be causing a problem.
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4 Posts |
Posted - Jun 25 2004 : 08:38:53 AM
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Hi SupraGuy. Thanks for your response. I can't figure out how to paste the schematic into this message, but I used the time delay relay schematic from Aaron's circuits. There is a diode across the relay activation terminals. The schematic shows a 12v input voltage, which coincides with the 12v electrical system on my bike. The only thing I changed is, I used a 12v - 30amp Bosc automotive relay (way more than I need for two bulbs) instead of the 9v relay called for. Could that be the problem?
John
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DELETED (Inactive)
56 Posts |
Posted - Jun 25 2004 : 11:51:28 AM
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I suspect that you may be overloading the drive current capability of the 555 timer IC.
To fix that, you'll need a resistor and a transistor. I'd suggest about 470 ohm resistor and a 2N2222 transistor should be adequate. (Although almost any general purpose NPN transistor should do.)
Connect the relay activation pins so that one is at +12VDC and the other is connected to the transistor collector
Connect the transistor's emitter to ground
Connect the 470 ohm resistor to the 555 timer IC output, and the other end to the transistor's base
This will limit output current from the 555 timer to about 20-25mA, which it should be able to handle perfectly well, and use the transistor to switch the larger load of the relay.
If that doesn't work, then you can start looking at dropping the supply voltage to the 555 IC. (Leave the relay and transistor connected to the 12V rails though, as this will still keep the relay switched with 12V.)
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Turn Signals
