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Topic starter
2020-03-08 1:44 pm
Thanks Bill, for fulfilling my request for an episode on these shift-registers.
I really needed a refresher on the 74HC165s.
But one thing I was wondering about was, I seem to remember reading that the maximum allowable current per pin was 20mA and the total allowable current for the IC was 80mA. So with red LEDs and 220Ω resisters, the maximum number of LEDs that can be lit at any one time is 4. 8 LEDs will be pulling 160mA.
Anyone, please correct me if I am wrong, although I tend to use 1kΩ resistors myself, no harm on erring on the safe side.
2020-03-08 3:58 pm
Very nice video Bill. ?
I especially liked the nice touch you added at the end by combining the two I/O systems.
I've been using the 74HC595 already in several projects. But I have yet to employ the 74HC165. But after watching your video I remembered that I had ordered some 74HC165 chips a while back just in case I needed more digital inputs. I looked in my drawer and found 30 of them still in plastic wrap. I'll have to get one out and play with it now.
You're such a distraction! Always getting me side-tracked onto other things. ?
DroneBot Workshop Robotics Engineer
James
2020-03-11 8:58 am
Great video, as usual. However, I was puzzled by Bill's remark, about using the Inverted Q7 on pin 7 of the 74HC165 instead of the Q7 on pin 9, "we won't get the full 8 bits". Can someone explain why this is and is there a way to use the Q7 on pin 9 and still receive the full 8 bits?
I have a small project that currently uses a 74HC165. I have it connected to an Arduino Pro Mini, but I am using the SPI library for communication. I have VCC on pin 16 of the 74HC165. Pin 15 and pin 8 are tied to GND. Pin 9 is my serial out which connects to pin 12 on the Pro Mini. Pin 10 is my serial input which is connected to Pin 9 of another 74HC165. Pin 1, the load pin, connects to any spare digital input on the Pro Mini (in my case, pin 7) and pin 2, the clock pin, connects to pin 13 on the Pro Mini.
My project seems to work, but I was wondering after watching Bill's video if I am doing something wrong?
Topic starter
2020-03-11 10:06 am
As Q7Inv(7) and Q7(9) are complimentary. From the datasheet figure 3 Serial Shift Mode if CP goes HIGH then Q7 also goes HIGH and Q7Inv remains LOW, therefore, the serial function of one of the pins is out of sync and the first bit will be lost.
But if I have understood the datasheet correctly, it may well be possible to use Q7(9) by having CP and CE(inv) in the reverse states.
Might be worth experimenting with!