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Posted on Oct 11, 2007

# Fairchild 555 Timer Configuration

I have a device which is controlled by a Fairchild KA555 timer.  At present it operates for 5 minutes at each hour, so I am presuming it's set up in astable configuration.

I need to replace the timing resisters so that I can vary both the On time and the Hold time.  It's been 20 years since my electronics training, and I simply can't remember the formulas.

The Capacitor on the board which is currently hanging off of Pin #6 is a 1000 microfarad electrolytic.

I would like to achieve an "On" time of 1 to 10 minutes.

I would like to extend the "Off" time variably from 1 hour up to 23 hours if possible, with one potentiometer.

If it is not possible to extend the "Off" time to that extent using only one potentiometer (due to the range of adjustment that would be required) then I need several values for RB that would give ranges from 1-4 hours, 4-8 hours, 8-16 hours, and 16-24 hours, so I can modify 4 different devices and proceed with some evaluative testing.

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• Posted on Oct 11, 2007
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Hi,
Yes, it is in an astable configuration.

You can find the 555 information here http://www.national.com/ds/LM/LM555.pdf

Look on page 8 for the astable information

in a nut shell, the charge time is determined by the addition of both resistors (Ra+Rb) while the discharge time by the one between the capacitor and the discharge pin (pin7), Rb.

Such long durations might be difficult to achieve due to capacitor leakage.

It would be better to add a counter at the output of the 555.

Enjoy,

Denis

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## Related Questions:

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Try it on another outlet, like in a dark bedroom without GFCI.
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Dec 20, 2011 • Hardware & Accessories
tip

### Setting Your Timer

1. Move the control lever to the OFF-CLEAR position for about 20 seconds. The red indicator light will go off and any previ- ous time settings will be cleared from memory.
Program Using "Quick" Method:
2. Move the control lever to the ON position. The Red indicator light will start fashing.
3. Rotate the time dial clockwise at least one click, stopping at the half hour nearest to the present time.
NOTE: During programming, be careful not to press the dial while turning it. If you press the dial, you will ac- cidentally set a wrong time.
4. Press the dial once to set the present time. The Red indicator light will go off.
5. Rotate the time dial clockwise to the frst desired ON time. The Red light will pulse momentarily with each click.
6. Press the dial once to enter the ON time. The light controlled by the switch timer will turn ON.
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For example, a) what voltage timer is needed, b) what Load are you controlling and c) how does timer mount?

Easiest solution is 60 minute repeat cycle timer.
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1) Tork 8600 cycle timer, or Tork ACT percent cycle timer
http://waterheatertimer.org/Tork-timers-and-manuals.html#8000
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http://waterheatertimer.org/Intermatic-timers-and-manuals.html#cycle

Oct 01, 2011 • Hardware & Accessories

### Can not set up my hydrofarm timer to come on for 1 min and off for 5 min.

You posted next to a photo showing hydrofarm analog timer with segments located on dial face.
Open following link for general look at setting analog timers.
http://waterheatertimer.org/How-to-set-timers.html

Analog timers have a minimum set time of 15 minutes because the trippers-or-pins-or-segments are made certain width.
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If you want 1 minute on and then 5 minutes off, and want to repeat that same cycle over and over throughout the day and night, you would need 240 set points.
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https://www.grainger.com/Grainger/cycle-timers/timers/electrical/ecatalog/N-8hbZ1z0q55s

If you want the cycle timer to operate certain hours only, then put ordinary 24-hour timer between the cycle timer and the load.

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Upvote the help.
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Utilitec makes 2 different plug-in timers.
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Utilitec 0144506 timer is small and rectangular with 5 buttons and slide switch located on top of timer. This timer can turn lights on-off once a day and has 1 outlet. 0144506 Instructions are given in steps shown below.
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Steps:
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-Unplug timer to set program.
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Hold down Time button
Press HOUR until current hour am-pm shows in display.
Hold down Time button
Press MIN button until current minute shows
Since this is a one-day repeat timer, no day program is available.

2) Program ON > this is when you want lamp to turn ON
Hold down ON button.
Press HOUR until ON hour with am-pm displays.
Hold down ON button.
Press MIN until ON minute displays.

2) Program OFF > this is when you want lamp to turn OFF
Hold down OFF button.
Press HOUR until OFF hour with am-pm displays.
Hold down OFF button.
Press MIN until OFF minute displays.

3) Set timer to operate
Make sure slide-switch on top of timer is set to 'Timer' to run program
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This is a countdown-type timer, for precise cooking times, etc. Press hour and minute buttons to set time.
Press start button to begin countdown.
Press hour and minute buttons same time to reset timer.
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For large image of timer:
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Aube T1032 is 500W 7-day timer with full range programming
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Aube T1032 buttons
Switch must be wire for display to show
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Open door to see buttons
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Open small door
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Set Sunrise-sunset parameters using tables that show in manual
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The above steps are 4 EZ steps for painting the Mona Lisa >>> please re-post question with detailed question

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Press SCAN/UP arrow or SCAN/DOWN arrow to change program time
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If you need further assistance follow up with a comment and please let me know and i will be glad to assist you further. Thanks, Midwest-tek

### Hello I lost my instructions for theej351c, can you help?

1. Move control lever to OFF-CLEAR for at least 5 seconds; red indicator light will go
off, and all previous time settings will be cleared from memory. (If timer fails to set, leave in off
position for 15 minutes.)
2. Move lever to ON. RED INDICATOR will start FLASHING.
3. Check a clock; then rotate time dial clockwise at least one click, stopping at the half
hour nearest to present time. NOTE: When rotating time dial, do NOT accidentally PRESS at
the same time. (While rotating dial, keep pressure, pulling out on the dial to avoid accidentally
setting an incorrect time.)
4. Press pushbutton once to enter present time. RED INDICATOR will go OFF, present
time has now been recorded.
5. Rotate time dial clockwise to desired ON time; RED light will PULSE momentarily
with each click.
6. Press pushbutton to enter ON time; controlled light(s) will turn on.
7. Rotate dial to desired OFF time.
8. Press pushbutton to enter OFF time; controlled light(s) will now be off.
9. Repeat Steps 5-8 for each addition ON/OFF period.
10. Continue to rotate time dial for at least 24 hours from the first ON time to complete
this program, at which time the RED INDICATOR light will come ON and stay ON,
indicating timer is in AUTOMATIC mode. NOTE: Dial does not rotate automatically
after setting to indicate time of day.

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