With a DPDT switch, I can switch the two data lines. I tried connecting the shields from the two computers together, the grounds two computers together, switching the D+ and D- lines with the DPDT switch, and leaving the VBus lines float, but for some reason it didn't work. The Lexmark printer seemed to need to see the +5 Volts. It had been many years since I read the USB standard (It was USB 1.0 back then) and I did not recall a function for the VBus beyond providing power to the peripheral, but in true experimentalist fashion, I added a transistor switch to supply VBus to the printer from whichever computer was connected, and the printer started working.
Click here to download the full size of the above Circuit.
I used a pair of transistors to "OR" the Vbus voltage from the two cables that go to the computers, but a while after building it, I realised that the "off" transistor could turn on because the backwards transistor (collector and emitter swapped) could still work, but with most transistor types with a lower gain. Modifications to prevent the "off" transistor from turning on would have resulted in a lot of parts, so, abut two years after building the switch, I tried a pair of Schottky diodes as David Hogg, a reader of this web site.
I used 1 Amp diodes instead of the lower current diodes because it will stand up better to abuse, and the 1 Am diodes will have a lower voltage drop than one with a lower current rating at a given current. The diodes work just fine in my office.
While on this subject, a fellow by the name of Jim Glasgow build a switch before he came across this web site. His switch used a four pole break-before-make switch. I think this is a superior method, if you can find such a switch. One possible hitch to switching the ground, is that there is no way to be sure that the ground connects first, so the data or Vbus conductors could connect first, thereby possibly subjecting the circuits in the printer or one of the computers to hazardous voltages. Its best to tie all the grounds together and only switch data and Vbus.
The common admonishments apply to this circuit: Keep the wires as short as practical,...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: