The 555 can be almost any type, they are all pin-compatible.Although some CMOS types may not have enough power to drive the transistor, in that case use an ordinary 555.working voltage should be increased to 25V if you decide to go with a 12V power source.Change the value of C1 for the desired output pulse.
For the timing use this equation:
T=1.1*(R1+P1)*C1 assuming R1 + P1 = 150K,then select C1 as follows:C1 = 6uF for each 1-second pulse width.For exampleif you want the pulse width to be 5 seconds, C1 should be 30uf or nearest value like 22 or 33uF.Additionally,P1 can adjust the rest.
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It is not a rare phenomenon that some USB devices attached to a computer during power-up remain invisible to the OS after booting. This concerns home-made devices during experiments and also some commercial ones. To make them visible again one has to disconnect the USB plug and reconnect it again. This leads to excessive contact wear of the USB connector. It would be nice to have a way to reconnect the device without mechanically unplugging it. A trivial solution based on buttons/switches or relays won't work because of their contact bouncing, which might confuse as device as well as the OS.
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In this Electronic Design Circuits Touch Switch project, a CMOS quad 2 input NOR gate IC is used as a latching circuit to switch a LED ON and OFF by physically touching the ON metal plate or OFF metal plate. The CD4001BC integrated circuit is a monolithic complementary MOS (CMOS) IC that are constructed with N- and P- channel enhancement mode transistors. Its input are protected against electrostatic discharge with diodes to VDD and VSS.
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A simple touch switch circuit using CD4011 is given here. The IC CD4011 is wires as a flip flop here. The 9, 13 pins of the IC works as the set and reset contacts respectively.CMOS ICs like 4011 require requires a very low current for controlling its gates. Since the pins 9 and 13 are connected to the positive via resistors R1 and R2, the logic gates of the ICs will be in high state. When we touch through the points A, B the gates of the IC will be closed and the output becomes low. This switches ON the transistor Q1 and the relay gets activated. When we touch through the points C, D the gates again becomes high and switches the transistor OFF. This makes the relay OFF. Thus by touching through the contact points A,B and C,D the appliance connected through the relay can be switched On and OFF.
Notes.
The circuit can be assembled on a general purpose PCB.
The circuit can be powered from 12V DC.
The IC must be mounted on a holder.
The relay can be a 12 V, 200 Ohm SPDT relay.
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