I am building a serial interface for a GPS module. This interface will have a "traditional" DB-9 connection, a USB-to-serial connection and a 5.5V power input. The GPS module will be in a separate enclosure some distance away.
I had considered designing this totally for USB, but it is for my server at home that has more unused COM ports than USB ports so I will design the serial interface around the MAX232.
Now my question about power: I could power the GPS module from USB with an FTDI Friend, and I have. But I'm more comfortable running it from a wall-wart, and if I connect it by DB-9 serial, I have to power it that way. I want to incorporate both the USB module and the DB-9, leaving it up to circumstance depending on where I use this.
I'd thought of using a 4066 switch to some LED's to indicate the state of the interface for troubleshooting (TxD, RxD and PPS) and I'm wondering if the 4066 is feasible for switching power inputs.
The USB module (an EM-406A) draws about 50 mA (rounded up from the datasheet value 44 mA.)
I would have the 4066 control pin connected to my 5.5V power inlet (where the wall-wart is connected) and controlling the +5V from the USB module. It would (or rather, I intend it to) shut off the +5V from the USB.
Is this feasible?
Best Answer
If you check the datasheet you'll see that the CD4066 has a rather high on-resistance. For instance, at 5V this is typical 470 ohm, maximum 1050 ohm (TI version). This is too much to switch any amount of current beyond something like 1 mA.
BTW, always design for worst case conditions, here the maximum value of 1050 ohm.