Read data input from shift register

tim687

The 74HCT164 is a serial to parallel converter.

Basically you set the state you want on that particular output using the two inputs and then raise the clock.

You need to do this 8 times to replace/set all 8 outputs

You need to read the value of the two data lines, and note them when the clock goes high.

You'll also need to check if the MR line is able to change, since it will reset the outputs.

Most 7 segment displays only need 4 bits, which means they could easily use the other 4 outputs for something else.

Mark

So you'd say I'd have to read out input A and B from the shift register and perform a (bit wise) AND operation onto them to get the input data?

The problem I'm having is that the two (serial coded) digits sometimes get swapped around.

The display definitely is a 8 bit display. It has got a total of 10 pins, 2 common anodes and 8 data pins.

The problem is however, that I will be using this in an IoT project, so I'm starting to get very tight with the available pins. I've freed up two pins using, how hilarious , a shift register.

That means that I only have a pin for the serial input A and the clock. I could free up more pins by using a shift in register, but I think that it would make the whole project to complex than it needs to be.

Thanks for your diagram though! I haven't searched for one to be honest

Thanks again!

Tim

So you'd say I'd have to read out input A and B from the shift register

Depends if they are using both inputs.

Sometimes they will tie one input high.

You'll need to read the 'input' and the clock.

It has got a total of 10 pins, 2 common anodes and 8 data pins.

Ahh yes I read it wrong sorry.

It will be multiplexing between the two digits and changing the data for each segment, so you do have your work cut out.

You'll also need to know what the data is for each segment, which means another input.

Don't forget the 5 Analogue pins are also digital (D14- D19)

mark

I've created a little schematic, the output pins of the shiftregister Q0-Q7 (in order) corresponds to the pins A-G and DP.

I've also figured out which pin controls which segment, but the strange thing is that there is no correlation between the serial input and the expected serial input according to my pin to segment research.

I got it working at some point, but only for a few numbers. (17, 21, 23, 25, 26, 27)

Is there something I might be missing?  

Is there something I might be missing? 

Bit hard to say from here ...

it could be timing, your code, change in how they clock it ...

Is this related to this.

Detect whether a pin is connected to GND

I posted a link where a local person has been able to detect the serial output from an Aircon unit.

https://nicegear.co.nz/blog/hacking-a-mitsubishi-heat-pump-air-conditioner/

It seems that many of them have a serial feed and I was wondering if your might have the same.

Mark

It indeed is related to the airport project. I'll check if is has one. That would make the job a lot easier. I don't see any UART pin in the schematic of the microprocessor however.

According to the datasheet of the micro, the chip doesn't have any SCI (Serial Communication Interface)

Besided checking both inputs, any other options?

Probably supposed to say SPI, not SCI ??

Probably supposed to say SPI, not SCI ??

Nope, the chip doesn't have SCI (serial/UART) and SPI according to my research.