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Electronics Forum / Basics / August 2007Simle LED driver
Hi, I have a simple 555 delayed timer and I wish to light up a LED when the timer starts and a relay off. At the end of the interval the LED should be off and the relay on. I made a simple circuit as follows: +------------+---+---------+---+------------+---------+-- VCC | | | | | .-. | | | | .-. | | | | .-. |4 |8 | |<-+ | |470 | | | .-------. | |1M '-' | | |10k | | '-' | | '-' | |3 | | | | | |------------+ | | | 2| 555 |7 | | led V -> | o----------| |--o----o | - | | | |6 | | | | | \ |+ | |--+ | | +---+ |_ o o === '-------' | | | | )| /-\33u |1 |5 47u|+ | ___ |/ | )| relay | | --- --- +--|___|--| | _)| | | ---10n /-\ 10k |> | +-- | | | | | | | GND GND GND GND | | |/ | +-| | |> | | | | +-------o | GND (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) But the LED stays ON at the end of the interval when the relay is switched ON. I have to add an iverter and modified the circuit as below: VCC -----o---------o---o------------o--------- o------------o | | | | | | | .-. | .-. | \ .-. |8 | |<-+ | | |_ o o | | .------. | |1M 10k| | )| | |470 | | '-' '-' )| relay '-' | |3 | | _)| | | |------------+ | | | | 555 |7 | | | | LED V -> | |--o----o | | | - | |6 | | | | | | \ | | |--+ | | +---+ o---| >O------ '------' | | | | | |/ |5 47u|+ | ___ |/ | | 4069 --- --- +--|___|--| | | ---10n /-\ 10k |> | +-+ | | | | | GND GND | | |/ | +-| | |> | | | | +-------o | GND (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) Is there any way not to light up the LED when the relay is switched on with just the two transistors? Allen > Hi, > [quoted text clipped - 79 lines] > > Allen Sorry about the screw-up, here is the second circuit again: VCC -----o---------o---o------------o---------o------------o | | | | | | | .-. | .-. | \ .-. |8 | |<-+ | | |_ o o | | .------. | |1M 10k| | )| | |470 | | '-' '-' )|relay '-' | |3 | | _)| | | |------------+ | | | | 555 |7 | | | | LED V -> | |--o----o | | | - | |6 | | | | | |\ | | |--+ | | +---+ o---| >O------ '------' | | | | | |/ |5 47u|+ | ___ |/ | | 4069 --- --- +--|___|--| | | ---10n /-\ 10k |> | +-+ | | | | | GND GND | | |/ | +-| | |> | | | | +-------o | GND (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) >> Hi, >> [quoted text clipped - 108 lines] > GND >(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) --- So, it looks like you want the relay to be ON and the LED to be OFF when power is down, and then when power comes up you want the relay to turn OFF and the LED to turn ON for a certain amount of time and then when that time expires you want the relay to turn ON and the LED to turn OFF for as long as power is up?  SignatureJF > On Mon, 27 Aug 2007 15:18:47 -0700, Allen Bong > [quoted text clipped - 123 lines] > > - Show quoted text - No, when the power is up the led will be ON and relay is OFF for a time determined by the 1M preset. When the time expires, the LED will be off and the relay turns ON. It operates exactly like a delay timer for electrical controls except that I have to put 8 of them on a PCB. When the power is off everything turns OFF. Allen > Hi, > [quoted text clipped - 81 lines] > > Allen You can get a lot simpler: +12 ------------------+------+ | | [Relay] [D2] D1 | |a 555 pin3]----+---|<---+------+ | a [470R] | [LED] | Gnd If you want to use a transistor driver for the relay: +12 ----------------------+ | /e [555 pin3]---+---[1K]---| PNP | \c [470R] | | +------+ [LED] | | | [Relay] [D1] | | |a Gnd ---------+------------+------+ In either circuit, when the 555 is "on" there is + at pin 3. That lights the LED, and keeps the relay off. When the 555 is "off", there is - at pin three. That keeps the LED off and the relay "on" (energized). Ed > > Hi, > [quoted text clipped - 118 lines] > > - Show quoted text - Thanks Ed, that seems to have solved all but one of my problems. Based on circuit #1, do you think the 555 would kick start reliably every time the power is switched ON? Regards, Allen >Thanks Ed, that seems to have solved all but one of my problems. >Based on circuit #1, do you think the 555 would kick start reliably >every time the power is switched ON? --- With RESET- tied to Vcc, in order to do that you'll have to make sure that the TRIGGER- input stays below 1/3Vcc until after the RESET- input rises above 1.0V. Additionally, the TRIGGER input must rise to >= 2/3Vcc before the one-shot times out. SignatureJF On Aug 28, 11:42 pm, John Fields <jfie...@austininstruments.com> wrote: > On Tue, 28 Aug 2007 00:14:57 -0700, Allen Bong > [quoted text clipped - 13 lines] > -- > JF Thanks very much John, I'll recalculated the values of the components on pins 2, 6 and 7 to make sure the interval of the TRIGGER is shorter than the minimum time interval of the one-shot. Allen |
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