Wednesday, September 24, 2014
Simple Mutifunction Timer Circuit
A timer is almost impossible without IC 555 or counter ICs such as CD4029 or CD4060. The circuit presented here uses an inverter instead for doing thc samc job.
As shown in the proposed multifunction timer circuit, gatc N1 along with C1, R1, VR1 and VR2 forms 21 monostable multivibrator. When S1 and S2, which are ganged, are in position 2, input at gate N1 is held low and hence the output of gate N1 becomes high. This high output charges C1 via A timer is almost impossible without IC 555 or counter ICs such as CD4029 or CD4060. The circuit pre- sented here uses an inverter instead for doing thc same job. As shown in the circuit, gatc N1 along with C1, R1, VR1 and VR2 forms 21 monostable multivibrator. When S1 and S2, which are ganged, are in position 2, input at gate N1 is held low and hence the output of gate N1 becomes high. This high output charges C1 via V series combination of R1, VR1 andVR2. At the same time output of gate N2, which is low, is given to gate N6 and the output of gate N6 becomes high.
The high output triggers the triac and the power is fed to the load. After a time period 0fT = 0.7 x C1 (R1 + VR1 + VR2), the output of gate N6 becomes low and the triac stops conducting. Thus this part of the circuit operates in monoshot mode.
When Sl and S2 are at position 1, the input of gate N6 is connected to the astable multivibrator built around gates N3 and N4.
Thus, the load is interrupted at regular intervals. Here VR3 is ganged with VR5, and VR4 is ganged with VR6 to generate a square wave. Duty cycle of the output can be varied by just removing the gang arrangement (because the at charging and discharging time will be different). Here gates N2 and N5 are as acting as buffers.
When Sl and S2 are in position 3, the input of gate N6 is grounded and so the output of N6 remains high as long as s the switches are in this position. Hence, the triac remains on and the current s flows continuously through the load. Finally, when Sl and S2 are in position 4, the input of N6 is connected to Vcc as a result of which the output re- mains at logic 0. The triac does not conduct and thus there is no current in the load.
330k pots arc calibrated for 0 to 60 seconds and 10M pots arc calibrated for 0 to 30 minutes. Thus, one can obtain any desired timing from 0 to 30 minutes. Use of tantalum capacitors will surely enhance the accuracy of the cir- cuit but at the same time the cost will also rise. Separate on/off switch is not required because stand-by mode consumption is only a few microamperes. In full load condition, the circuit consumes around 5 to 6 mA current ensuring a long life for the battery.
This kind of time switch can be used r as a timer for washing machines, heat- ers and for process control involving short timing etc. The circuit can be easily wired onla general-purpose PCB. It costs around Rs 50, without power supply.
As shown in the proposed multifunction timer circuit, gatc N1 along with C1, R1, VR1 and VR2 forms 21 monostable multivibrator. When S1 and S2, which are ganged, are in position 2, input at gate N1 is held low and hence the output of gate N1 becomes high. This high output charges C1 via A timer is almost impossible without IC 555 or counter ICs such as CD4029 or CD4060. The circuit pre- sented here uses an inverter instead for doing thc same job. As shown in the circuit, gatc N1 along with C1, R1, VR1 and VR2 forms 21 monostable multivibrator. When S1 and S2, which are ganged, are in position 2, input at gate N1 is held low and hence the output of gate N1 becomes high. This high output charges C1 via V series combination of R1, VR1 andVR2. At the same time output of gate N2, which is low, is given to gate N6 and the output of gate N6 becomes high.
The high output triggers the triac and the power is fed to the load. After a time period 0fT = 0.7 x C1 (R1 + VR1 + VR2), the output of gate N6 becomes low and the triac stops conducting. Thus this part of the circuit operates in monoshot mode.
When Sl and S2 are at position 1, the input of gate N6 is connected to the astable multivibrator built around gates N3 and N4.
Thus, the load is interrupted at regular intervals. Here VR3 is ganged with VR5, and VR4 is ganged with VR6 to generate a square wave. Duty cycle of the output can be varied by just removing the gang arrangement (because the at charging and discharging time will be different). Here gates N2 and N5 are as acting as buffers.
When Sl and S2 are in position 3, the input of gate N6 is grounded and so the output of N6 remains high as long as s the switches are in this position. Hence, the triac remains on and the current s flows continuously through the load. Finally, when Sl and S2 are in position 4, the input of N6 is connected to Vcc as a result of which the output re- mains at logic 0. The triac does not conduct and thus there is no current in the load.
330k pots arc calibrated for 0 to 60 seconds and 10M pots arc calibrated for 0 to 30 minutes. Thus, one can obtain any desired timing from 0 to 30 minutes. Use of tantalum capacitors will surely enhance the accuracy of the cir- cuit but at the same time the cost will also rise. Separate on/off switch is not required because stand-by mode consumption is only a few microamperes. In full load condition, the circuit consumes around 5 to 6 mA current ensuring a long life for the battery.
This kind of time switch can be used r as a timer for washing machines, heat- ers and for process control involving short timing etc. The circuit can be easily wired onla general-purpose PCB. It costs around Rs 50, without power supply.
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