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https://github.com/mcauser/micropython-74hc595

MicroPython driver for 74HC595 shift registers
https://github.com/mcauser/micropython-74hc595

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MicroPython driver for 74HC595 shift registers

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README 

        
# MicroPython 74HC595



A MicroPython library for 74HC595 8-bit shift registers.



There's both an SPI version and a bit-bang version, each with a slightly

different interface. See below.



![demo](docs/demo.jpg)



### Installation



Using mip via mpremote:



```bash

$ mpremote mip install github:mcauser/micropython-74hc595

$ mpremote mip install github:mcauser/micropython-74hc595/examples

```



Using mip directly on a WiFi capable board:



```python

>>> import mip

>>> mip.install("github:mcauser/micropython-74hc595")

>>> mip.install("github:mcauser/micropython-74hc595/examples")

```



Manual installation:



Copy `src/sr74hc595_bitbang.py` and `src/sr74hc595_spi.py` to the root directory of your device.



## SPI Version



You can use either HSPI or SPI. This version is significantly faster than the

bit-bang version, but is limited to writing whole bytes of data.



### SPI Example



**Basic Usage**



```python

from machine import Pin, SPI

from sr74hc595 import SR74HC595_SPI



spi = SPI(1, 100000)

rclk = Pin(5, Pin.OUT)



oe = Pin(33, Pin.OUT, value=0)    # low enables output

srclr = Pin(32, Pin.OUT, value=1) # pulsing low clears data



sr = SR74HC595_SPI(spi, rclk, 2) # chain of 2 shift registers



sr.pin(2,1)  # set pin 2 high of furthest shift register

sr.pin(2)    # read pin 2

sr.pin(2,0)  # set pin 2 low



sr.toggle(8) # toggle first pin of closest shift register



sr[0] = 0xff # set all pins high on furthest shift register

sr[1] = 240  # set half pins high on closest shift register

sr[1]        # read pins



oe.value(0)  # disable outputs

oe.value(1)  # enable outputs



# pulse to clear shift register memory

srclr.value(1)

srclr.value(0)

```



### SPI Methods



Construct with a reference to `spi` and the `rclk` pin used for latching and an

optional number of cascading shift registers.



Pins `srclr` and `oe` are optional.

If you don't need to clear the outputs, connect `srclr` to vcc.

If you don't need to disable the outputs, connect `oe` to gnd.



```python

__init__(spi, rclk, length=1, srclr=None, oe=None)

```



Read the boolean value of a pin. First pin is index `0`. If you are cascading shift

registers, the first pin of the second shift register is index `8` and so on. Index

`0-7` are the furthest away shift register from the serial data in.



```python

pin(index)

```



Writes a boolean value to a pin. This updates the internal buffer of pin values then

writes all of the values to each shift register in the chain.



```python

pin(index, value, latch=True)

```



This toggles a single pin by index. Helper for reading a pin then writing the opposite

value.



```python

toggle(index, latch=True)

```



This lets you treat the class like a list, where each index represents a whole shift

register. Returns an 8-bit value for the shift register by index, where lowest index

is furthest away.



```python

__getitem__(index)

```



Write an 8-bit value to a shift register at the given index.



```python

__setitem__(index, value)

```



Private method for sending the entire internal buffer over SPI.



```python

_write(latch=False)

```



Private method for pulsing the `rclk` pin, which latches the outputs from the shift

register to the storage register and makes the outputs appear.



```python

_latch()

```



## Bit Bang Version



This version lets you have greater control over sending individual bits of data

at the expense of the performance you get using SPI.



### Bit Bang Example



**Basic Usage**



```python

from machine import Pin

from sr74hc595 import SR74HC595_BITBANG



ser = Pin(23, Pin.OUT)

rclk = Pin(5, Pin.OUT)

srclk = Pin(18, Pin.OUT)



# construct without optional pins

sr = SR74HC595_BITBANG(ser, srclk, rclk)



sr.clear()  # raises RuntimeError because you haven't provide srclr pin

sr.enable() # raises RuntimeError because you haven't provide oe pin



# reconstruct with all pins

oe = Pin(33, Pin.OUT, value=0)    # low enables output

srclr = Pin(32, Pin.OUT, value=1) # pulsing low clears data



sr = SR74HC595_BITBANG(ser, srclk, rclk, srclr, oe)



sr.bit(1)  # send high bit, do not latch yet

sr.bit(0)  # send low bit, do not latch yet

sr.latch() # latch outputs, outputs=0000_0010



sr.bit(1, 1) # send high bit and latch, outputs=0000_0101

sr.bit(0, 1) # send low bit and latch, outputs=0000_1010



sr.bits(0xff, 4) # send 4 lowest bits of 0xff (sends 0x0f), outputs=1010_1111



sr.clear(0) # clear the memory but don't latch yet

sr.latch()  # next latch shows the outputs have been reset



sr.bits(0b1010_1010, 8) # write some bits

sr.clear()  # clear the memory and latch, outputs have been reset



sr.enable()  # outputs enabled

sr.enable(0) # outputs disabled

```



### Bit Bang Methods



Construct with references to each of the pins needed to write to the shift register(s).



Pins `ser`, `srclk` and `rclk` are required. Pins `srclr` and `oe` are optional.

If you don't need to clear the outputs, connect `srclr` to vcc.

If you don't need to disable the outputs, connect `oe` to gnd.



```python

__init__(ser, srclk, rclk, srclr=None, oe=None)

```



Writes a single value and can optionally latch to make it visible.



```python

bit(value, latch=False)

```



Write multiple (`num_bits`) values from the supplied value and optionally can latch.



```python

bits(value, num_bits, latch=False)

```



Pulses the `rclk` pin to latch the outputs. Without this, all of the bits you have

written are remain hidden.



```python

latch()

```



Clears the shift register memory by pulsing the `srclr` pin. You will get a runtime

error unless you have provided this pin on construct.



```python

clear(latch=True)

```



Toggles the output of the shift register by toggling the output enable (`oe`) pin.

You will get a runtime error unless you have provided this pin on construct.



```python

enable(enabled=True)

```



Private method for pulsing the `srclk` pin, which tells the shift register to read

the current state of the `ser` pin and copy it to the shift register memory.



```python

_clock()

```



## Chaining



You can connect multiple 74HC595 shift registers together to form a chain.



Connect each shift registers `rclk`, `srclk`, `oe` and `srclr` together.

If you don't need to disable outputs, you can tie each `oe` to ground.

If you don't need to clear any outputs, you can tie each `srclr` to vcc.



Your micro controller provides data to just the first shift registers `ser` pin.



The `QH\`` output pin on the first shift register goes into the next shift register

`ser` pin and so on.



When clocking in data, the values appear on the closest shift register to the

micro controller first, before overflowing into each chained shift register.



## Parts



* [TinyPICO](https://www.tinypico.com/)

* [74HC595 DIP-16](https://s.click.aliexpress.com/e/_DnLBdpL)

* [74HC595 breakout](https://s.click.aliexpress.com/e/_Der4vyZ)



## Connections



TinyPICO       | 74HC595

-------------- | -------

3V3            | VCC

G              | GND

G (or a pin)   | OE

23 MOSI        | SER

18 SCK         | SRCLK

5              | RCLK

3V3 (or a pin) | SRCLR



Pin   | Name                   | Description

----- | ---------------------- | -----------

OE    | Output Enable          | Active low. Drive high to disable outputs.

SER   | Serial Input           | Serial data sent LSB first.

RCLK  | Storage Register Clock | Pulse to latch data to outputs.

SRCLK | Shift Register Clock   | Serial input is read on rising edge.

SRCLR | Shift Register Clear   | Active low. Drive high to clear contents.

QA-QH | Outputs                | 8 output pins

QH\`  | Serial Output          | Connect to the next 74HC595 SER pin



## Links



* [TinyPICO Getting Started](https://www.tinypico.com/gettingstarted)

* [micropython.org](http://micropython.org)

* [74HC595 datasheet](docs/sn74hc595n.pdf)



## License



Licensed under the [MIT License](http://opensource.org/licenses/MIT).



Copyright (c) 2021 Mike Causer