Gadget Freak

Two more inspirations for designing your own circuits - taken from our Design Ideas section.

They involve a hot-swap serial-interface circuit allows two computers to monitor all the traffic on an RS-232 port and a laser-diode-clamp circuit that protects against overvoltages.

Hot-swap circuit allows two computers to monitor an RS-232 channel, courtesy of Jeff Patterson, All Weather Inc, Sacramento, CA; Edited by Charles H Small and Fran Granville

Improved laser-diode-clamp circuit protects against overvoltages, courtesy of James Zannis, Baulne-en-Brie, France; Edited by Charles H Small and Fran Granville

Hot-swap circuit allows two computers to monitor an RS-232 channel
The hot-swap serial-interface circuit in Figure 1 allows two computers to see all of the communication between each computer and each device on the communication network for that serial port.

This circuit allows each computer to determine what the other is doing and receive all of the data from the peripheral device. Only one device can transmit at a time; otherwise, the transmitted data becomes corrupted.
Read the full Circuit Design Idea

Improved laser-diode-clamp circuit protects against overvoltages
Expensive semiconductor laser diodes have no tolerance for fast voltage or current transients. To minimize the risk of damage, a standard JFET-clamp circuit shorts the laser when there is no supply voltage, thus protecting it against such transients (Figure 1).

When the negative supply rail comes up, the JFET turns off. This circuit is effective for low-power laser diodes but may not be so for diodes with power dissipation greater than 150 mA. The maximum cutoff current of the JFET sets this limit.
Read the full Circuit Design Idea