pinstatus LEDs
Erlend
Posts: 612
In a project I am doing I would like to have LEDs tell the status of all prop i/o pins, irrespectly of wether thay are configured as input or output. This means the LED driver must have a high input impedance, be controlled by individual digital inputs, and be 3.3V compatible. I need advice about what would be a good multichannel driver chip - and where it can be obtained? I have a few 4007, but they are only 4-channel - which means a lot of soldering and PCB space. Cannot find it in the google jungle.
Erlend
Erlend
Comments
These can be powered by 3.3v to behave as 3.3v logic, or powered at 5.0v with 3.3 logic inputs to output 5 volt logic levels. Indivdual ICs have different capacities to provide the extra power you need.
But the real concern is if you want these to be bi-directional to all 32 i/o pins and provide LEDs in both directions. It might be easier to have each i/o pin drive a two-color LED and have each i/o pin provide a bi-directional buffer as well.
Generally bi-directional buffers can only switch directions of banks of 4 bits, 8 bits, and so on. If you want each and every i/o pin independent, you may have to provide another scheme.. such as an individual MOSfet as a bi-directional i/o buffer on each and every pin.
244 is an octal buffer with enable/direction inputs (so you can easily turn the LEDs all off if you want). The 74HC
series goes down to 2V supply and is cheap.
Note that when pins are inputs the threshold voltages of the Prop and the 245 will not be the same so when
used as analog inputs the LED state won't necessarily match the Prop's INA register - proper logic levels
would be fine though.
[though the prev poster's suggestion of the LVC family would handle higher currents if the LEDs aren't so bright,
the HC family can do about 5mA at 3V3, LVC 24mA]
Although I do not need the bidirection function, this looks perfect. A nice feature to be able to switch them all off too. Now I need to find where to buy a handful.
Erlend