Serial/parallel shift register

Thread Starter

Archaeus

Joined Sep 10, 2016
34
I have little knowledge regarding shift registers and would like to understand them better. I'm working on a simple RF project and thought perhaps they could be implemented. What I'd like to know is if a parallel-serial ic such as the 4014 would be able to be interfaced with a complimentary serial-parallel register (perhaps a 74164?). I am wondering if a parallel-serial could transmit multiple parallel input signals serially over to an RF receiver, then be converted back to parallel through serial-parallel? Is this doable with those IC's without use of a microcontroller? I would imagine matching clock frequencies is important if so? Thank you.
 

AnalogKid

Joined Aug 1, 2013
8,596
Is this doable with those IC's without use of a microcontroller?
Yes, but ...
I would imagine matching clock frequencies is important if so?
Very. You are going down the path or re-inventing the UART, something many young designers go through. A UART is a single-chip parallel-to-serial and serial-to-parallel communication system on a single chip. It uses a clock rate that is 16 times faster than the rate the data bits are being shifted. This allows there to be a small difference in the transmit and receive clock rates and still capture the data bits accurately. For a system based on simple shift registers, you have to transmit the data on one wire and the clock on another wire so the receiver is perfectly synchronized to the transmitter. You also have to add logic to tell the transmitter when to load and when to shift, and for the receiver to figure out that it has a complete data byte ready to be read. Before UARTs were invented this took dozens of chips.

Another way is to use specialized remote control chips that take care of all of the logic and are easier to use than a UART. Holtek makes the HT12. It can send 4 data bits relatively slowly, but with very few external parts. Also, it is addressable, so you can have multiple parts on a common transmission bus and each part has a unique address.

ak
 

MrChips

Joined Oct 2, 2009
21,877
Let's forget serial-parallel converters for the moment, chips are available to do that.

What you need to consider is the RF portion and how you are going to modulate the RF.
What RF frequency are you considering? What data rates are you aiming to transmit?
What is the distance between RF transmitter and receiver?
Have you considered using commercial RF modules such as Linx?
 

Thread Starter

Archaeus

Joined Sep 10, 2016
34
Thank you both for the comments. Ak, thank you for putting into perspective the exact ideas that were popping into my head. I am just a hobbyist, but glad you understood and pointed me to study UART. Good to know I was at least heading in the right direction. I have worked with the ht12e/d chips before for my first simple RC car and they work very well (I just read data sheet enough to configure. No idea how it worked). Like you said, they are 4 bit and I have to order them online with high shipping rates for what they are price wise. My local store has shift registers, so that's why I wanted to get my hands dirty and see what could be done.

Just to clarify a little on what I'm trying to transmit. I am not looking into sending digital word bytes that require a start/stop code etc. I was wondering if I could basically use the data pins on the parallel chip to send high/low (remote control on/off) levels to the transmitter simultaneously and or randomly. I might have one remote switch send a high to a data pin for 3 seconds high, then another pin low for 5 sec, another high for 10 sec etc. All randomly applying high/low signals to the inputs to be sent and extracted back to the same parallel ports on the receiving end. So the transmission can be a continual load, shift, read application. Does this make it more simple or achievable without too many external components? Would a clock on the same frequency independently provided to each chip work?

MrChips, I was just planning on using a generic 433mhz Tx/Rx set from robot shops. Distance no more than 50 ft or so. What would be an appropriate bit rate to achieve the above mentioned application? Assuming it's even achievable with my options.
 

MrChips

Joined Oct 2, 2009
21,877
If high data rates is not an objective, sending UART data at 4800 baud should do the trick. No additional serial-to-parallel chips required.
 
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