Showing posts with label timer. Show all posts
Showing posts with label timer. Show all posts
Tuesday, September 3, 2013
9 Sec Timer with LED Indication and Control Relay
The electronic circuit provides a visual time 9 second delay using ten LED before control by closing a 12 Vdc relay. That the reset switch has closed, IC 4017 decade counter will be reset to zero count which illuminates the LED driven from pin 3. IC 555 timer output at pin 3 will be high and the voltage at pins 6 and 2 of the timer will be a little less than the lower trigger point, or about 3 Vdc.
9 Sec Timer with LED Indication and Control Relay Circuit Schematic
That time the switch is opened, the transistor in parallel with the timing capacitor (22uF) is shut off allowing the capacitor to begin charging and the IC 555 timer circuit to produce an approximate one second clock signal to the decade counter. The counter advances on each positive going change at pin 14 and is enabled with pin 13 terminated low. When the 9th count is reached, pin 11 and 13 will be high, stopping the counter and energizing the relay. Longer delay times can be obtained with most capacitor or most resistor at pins 2 and 6 of the IC 555 timer.
9 Sec Timer with LED Indication and Control Relay Circuit Schematic
Tuesday, April 9, 2013
Up Down Timer Circuit For A Power Antenna
This up/down timer circuit was designed to control a power antenna on a late-model vehicle. Normally, this vehicle uses a body computer to control the antenna. However, the person who owned the vehicle wanted to install his own high powered audio stereo system. The original stereo system was tied in with the body computer and this meant that a separate antenna controller was required for the after-market sound system. Also, the power antenna fitted did not have limit switches inside, hence the need for a timed control circuit. Heres how the circuit works. first, assume that the radio antenna control output is not switched on - ie, the radio is switched off.
In that case, relay RLYC will be off and so relay RLYA will also be off, as is the motor. Conversely, when the radio is switched on, the radio antenna control output line switches to +12V. And when that happens, RLYC closes its contacts and applies power to the circuit. As a result, C2 (330OF) quickly charges via D4, while Q4 is biased on via D5 and R5. This ensures that Q3 and relay RLYB remain off. At the same time, Q2 is is turned on, thus turning on RLYA and applying power to the motor. This drives the antenna in the up direction. During this time, C1 charges via R2.
Circuit diagram:
Up/Down Timer Circuit Diagram
When the voltage across the capacitor reaches +8.1V, Q1 turns on via ZD1 and so Q2 turns off and switches off the relay - ie, this gives the "up" timeout. Using the values shown for C1, R2 and ZD1 gives an "up" duration of approximately 6 seconds - long enough to fully extend the antenna. D1 discharges C1 (via resistor R1) when the +12V supply is later removed.
When the radio is switched off (or a CD placed into the stereo unit), the radio antenna control output switches back to 0V. This does several things: first, it turns Q4 off and this allows Q3 to turn on due to the stored charge in C2. Q3 and RLYB now turn on for about six seconds - ie, while C2 discharges via R4 - and this switches power to the motor in the opposite direction to drive the antenna down. Diodes D4 and D5 are there to prevent C2 from discharging back via the circuitry around on Q1 and Q2.
Author: Peter Howarth - Copyright: Silicon Chip Electronics
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