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Help with 5,10,15,20,25,30 min countdown timer

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taranakiguy

New Member
I have bee trying to find a circuit diagram for 5,10,15,20,25,30 minute selectable countdown timer. the closest I have found is this one here.

Descriptipn:
A switched timer for intervals of 5 to 30 minutes incremented in 5 minute steps.
Notes:
Simple to build, simple to make, nothing too complicated here. However you must use the CMOS type 555 timer designated the 7555, a normal 555 timer will not work here due to the resistor values. Also a low leakage type capacitor must be used for C1, and I would strongly suggest a Tantalum Bead type. Switch 3 adds an extra resistor in series to the timing chain with each rotation, the timing period us defined as :

Timing = 1.1 C1 x R1

Note that R1 has a value of 8.2M with S3 at position "a" and 49.2M at position "f". This equates to just short of 300 seconds for each position of S3. C1 and R1 through R6 may be changed for different timing periods. The output current from Pin 3 of the timer, is amplified by Q1 and used to drive a relay.

Parts List:

Relay 9 volt coil with c/o contact (1)
S1: On/Off (1)
S2: Start (1)
S3: Range (1)
IC1: 7555 (1)
B1: 9V (1)
C1: 33uF CAP (1)
Q1: BC109C NPN (1)
D1: 1N4004 DIODE (1)
C2: 100n CAP (1)
R6,R5,R4,R3,R2,R1: 8.2M RESISTOR (6)
R8: 100k RESISTOR (1)
R7: 4.7k RESISTOR (1)
Circuit by Andy Collinson
Source: zen's circuit directory



Problem is I want to cast the whole thing in resin so as to make it waterproof so I would like to make the selector work via magnetic switch (as well as the start/stop switch) also I would like to include LEDs to indicate which setting is selected, can anybody help with the design for me?

Ultimately it will need to control a relay that will start a 200w 12v motor which will need to run for the selected time and then shut off
 
Last edited:

Boncuk

New Member
Hi,

you could use a modification of tarnankiyguy's design. Just use the initial timer setting of five minutes and connect the timer output to a decimal counter (HCF4017). You'll have to adjust the basic 5 min setting and the rest will be as accurate as the basic setting. That way you might use 9 different time settings.

Using a DIP-switch to select the desired time will not be a problem. Otherwise use a single pole 12 throw rotary type switch and limit it to ten positions. (One position for OFF)

Boncuk
 

steveo

New Member
Did you have a reply in regards to using a reed switch's to activated the timing circuit at diferent times that is required


Help with 5,10,15,20,25,30 min countdown timer
I have bee trying to find a circuit diagram for 5,10,15,20,25,30 minute selectable countdown timer. the closest I have found is this one here.

Descriptipn:
A switched timer for intervals of 5 to 30 minutes incremented in 5 minute steps.
Notes:
Simple to build, simple to make, nothing too complicated here. However you must use the CMOS type 555 timer designated the 7555, a normal 555 timer will not work here due to the resistor values. Also a low leakage type capacitor must be used for C1, and I would strongly suggest a Tantalum Bead type. Switch 3 adds an extra resistor in series to the timing chain with each rotation, the timing period us defined as :

Timing = 1.1 C1 x R1

Note that R1 has a value of 8.2M with S3 at position "a" and 49.2M at position "f". This equates to just short of 300 seconds for each position of S3. C1 and R1 through R6 may be changed for different timing periods. The output current from Pin 3 of the timer, is amplified by Q1 and used to drive a relay.

Parts List:

Relay 9 volt coil with c/o contact (1)
S1: On/Off (1)
S2: Start (1)
S3: Range (1)
IC1: 7555 (1)
B1: 9V (1)
C1: 33uF CAP (1)
Q1: BC109C NPN (1)
D1: 1N4004 DIODE (1)
C2: 100n CAP (1)
R6,R5,R4,R3,R2,R1: 8.2M RESISTOR (6)
R8: 100k RESISTOR (1)
R7: 4.7k RESISTOR (1)
Circuit by Andy Collinson
Source: zen's circuit directory


Problem is I want to cast the whole thing in resin so as to make it waterproof so I would like to make the selector work via magnetic switch (as well as the start/stop switch) also I would like to include LEDs to indicate which setting is selected, can anybody help with the design for me?

Ultimately it will need to control a relay that will start a 200w 12v motor which will need to run for the selected time and then shut off
 
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