USB Printer Share Switch

This simple device allows two computers to share a single USB printer or some other USB device, such as an external flash drive, memory card reader or scanner. A rotary switch selects the PC that you wish to use with the USB device, while two LEDs indicate the selected PC.

The most common way to share a USB printer between two PCs is to use one machine as a print server. However, that’s not always convenient because it means that the server PC must always be on if you want to print something.

Picture of the project:

That can be a real nuisance if you just want to quickly fire up the other machine and print something out. It also means that the two PCs must be networked together, either via a hub/router or directly via an ethernet crossover cable. Another way is to use a dedicated USB print server. However, as before, this must be connected to an ethernet network, along with the PCs. Such devices also need their own power supply, generally cost well over $100 and are overkill if you just want to share a single USB printer between two computers for occasional printing in a home set-up.

Parts layout:

That’s where this simple device comes in. It’s basically a 2-way switch box that lets you manually switch your USB printer from one PC to the other, as required. The switching is performed using a rotary switch, while two LEDs on the front panel indicate which PC has been connected to the printer. This method has several advantages. First, you don’t need to network your two computers. Second, you can print from either machine with the other turned off. And third, the device doesn’t need a power supply.

Circuit diagram:

The circuit uses switch poles S1a-S1c to select either USB socket CON1 or CON2 and connect its pins through to CON3. The fourth pole (S1d) selects either LED1 or LED2, to indicate which PC has been selected.

Source: Silicon Chip14 April 2009

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Remote controlled appliance switch circuit

Here is a versatile remote controlled appliance switch that can ON or OFF any appliance connected to it using a TV remote.






IR remote sensor IC TSOP 1738 is used for receiving the signal. Normally when no signal is falling on IC3 the output of it will be high.This makes Q1 OFF.When a signal of 38 KHz from the TV remote falls on the IC3 its output goes low.This makes Q1 conduct and a negative pulse is obtained at pin 2 of IC 1 NE 555.Due to this IC1 wired as a monostable multivibrator produces a 4 Sec long high signal at its out put.This high out put is the clock for IC 2 which is wired as a Flipflop and of , its two outputs pin 3
goes low and pin 2 goes high.The high output at pin 2 is amplified to drive the relay .For the next signal the outputs of IC2 toggles state. Result, we get a relay toggling on each press on the remote.Any appliance connected to this circuit can be switched ON or OFF.




Notes .

* Before wiring the circuit make sure that the carrier frequency of the
TV remote you have is 38 kHz.For that wire the sensor part only ,point your
remote to the TSOP1738 and press any switch.If out put of TSOP1738 goes
low then OK, your remote is of 38Khz type.Nothing to worry almost all TV
remote are of this type.

* You can use any switch of the remote because for any switch the code only changes,
the carrier frequency remains same.We need this carrier frequency only.

* Assemble the circuit on a good quality PCB or common board.

* The appliance can be connected through NO or NC and C contacts of the relay .

* Use a regulated 6V power supply for the circuit.

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