I want to build a timer which, when activated, causes an LED to flash
(approx 0.5 to 1 hz, but the precise frequency is not that important)
for 30, 60, 90 or 120 minutes (adjustable). Ideally, power supply
would be 1.5 to 3V. Since I am new, simplicity would be appreciated.
Thanks for any help.
For simplicity, use a lamp timer like Intermatic TN111C Lamp
& Appliance Timer ($6.49 at Amazon.Com). Plug a 5V DC regulated
wall wart supply (CAT# DCTX-512 $3.50 at Allelcetronics.com)
into it, and connect the supply to a blinking LED (CAT# LED-4
$0.90 for 2 at allelectronics) through a 100 ohm resistor.
------ --------
| |---| +|---[100R]---[LED]---+
|TN111C| |DCTX-512| |
| |---| -|--------------------+
------ --------
To operate, plug the timer in and set the ontime and off
time buttons 30, 60 90 or 120 minutes apart. Then turn the
timer dial until the LED starts to blink. It will blink
for the duration you choose, then stop. It will repeat the
next day and every day thereafter, unless you unplug it.
If you want a little more complexity, the TN111C can
be replaced by a kit: QK152 $12.95 at
http://store.qkits.com/moreinfo.cfm/QK152
It requires a 12 volt power supply (CAT# PS-1251 $8.50 at
allelectronics) and your circuit would change:
+---------------+
| |
------- | ---------- |
| +|-+-| NC|--+
| 12V | | Qk152 |
| Wall | | COM|---[1K]---+
| Wart | | | |
| -|-+-| NO| [LED]
------- | ---------- |
| |
+-----------------------+
This will increase your cost, but you'll get a little more
electronics experience assembling the kit and adjusting the
timing, and it won't need to be unplugged to prevent it from
turning on again the next day. Later on, once you have
that working as you like, the 12V supply could be replaced
with a DC-DC converter to allow operation from 3 volts
or 1.5 volts. You would likely want to modify the Q152 as well
to eliminate the relay which reduces current drain.
Ed