EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: BurnedResistor on May 08, 2017, 06:11:17 am
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Hello All,
I am working on a demonstrative project which includes a tristated busses (A total of 48 lines). I thought it would be neat to have two leds for each wire to indicate it's state: one to light up if it is tristated, and one indicating its logic state (on if high, off if low, off if tristated). Detecting tristating is easy enough with a window comparator and equal pull ups and pull downs to hold the bus at 2.5 v. However, because of the large number, it would e great to have this functionality within a single chip.
I found a Linear Technology Part: http://cds.linear.com/docs/en/datasheet/1042fa.pdf (http://cds.linear.com/docs/en/datasheet/1042fa.pdf)
It is a window comparator with an output that goes high if it is within the window, which would be my tristate led, and an output which goes high if it is above the window, which would by my logic led.
However, it is not available in a small smd form factor, nor is it available at mouser. At prices of one euro per part it is also rather expensive.
Anybody know of any other similar chips which could do this? Speed is not very important, as it is only really used at low frequencys where the change in LED is visible. 5V Supply, and would be great if it could drive an led by itself!
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Because it is split up on 4 different busses, I might only need one window comparator per bus, and have only one tristate led per bus.
Maybe hook up the window comparator to one of the lines, and then leds directly to all of them. The output of the comparator could sink all the the leds, so when it is high (tristated), all of the LEDs are off. Might need some buffers as sinking 16 leds in one comparator is not that good of an idea!
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Possibly PSOC, one part to do all the detection, see attached tool shot,
and another for LED driving.
PSOC code should take ~ 30 - 40 lines of code max, and a serial component
to drive LEDs, a serial to parallel converter chip. Could use another PSOC if drive
currents did not exceed PSOC total allowed per port Vddport current. Couple
them using I2C component.
AN72382 is pertinent application note on total allowed current limits for GPIO.
Code can setup amount of hysteresis.
Regards, Dana,