All I2C cards published so far in this magazine (see References/bus-fuse) are normally powered by the 5 V supply in the PC via the 6-way DIN socket on the 12C PC insertion card. A drawback of this arrangement is that the 5 V supply in the PC is at risk of being short-circuited by a fault on any of the I2C cards connected. Since most PC power supplies are capable of supplying very high currents at the 5-V output (20+ A is typical!), short circuits can cause a lot of smoke and annoyance. The circuit shown here protects your costly N, hardware by inserting a fast I A glass fuse in the 5 V supply line between the I2C interface card in the PC and the first I2C card in the chain. Alternatively, for even better security, a fuse card may be inserted into every cable that connects two I2C boards.
Two LEDs are fitted on the fuse card to signal the presence of the 5 V supply voltage ahead of and behind the fuse. The LEDs cause an additional current consumption of about 20 mA. The printed circuit board shown allows five fuse cards to be built.
- R1. R2 = 330 Q
- D1, D2 =LED, 3 mm, red
- K1. K2 = 6-way mini-DIN socket for PCB mounting
- Fl = fuse, 1 A (fast), with holder for PCB mounting
PCB Ref. 934016
- I2C interface for PCs. Elektor Electronics February 1992.
- ADC/DAC and I/O for I2C bus. Elektor Electronics March 1992
- I2C LED display. Elektor Electronics June 1992.
- I2 Opto/relay card. Elektor Electronics February 1