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Voltage-Level Data-Output RXB6
#1
I use the RXB-6 with the ATTiny85 like on this page https://manual.pilight.org/en/electronics-wiring
with an Raspberry 3.

Is that wiring only "symbolic" - should an Level-Shifter/Voltage divider installed between Attiny and GPIO-Connector?
The 5V DC is connected to sender and receiver, so the data output of the receiver can reach a level over 3.3V? I read in some other threads that this can damage the PI. I measured some "noise-pulses" up to 4.5V now - can this damage the PI?

I´ve tested with voltage divider and a RX-MK-5V receiver. That works - once the terrible range of reception with this module ;-).
With RXB6 and voltage divider next the Attiny i´ve received nothing.

I would also buy the pilight-PCB, but the PI is placed in a 19"-Rack - with the hooked PCB I think there is no reception inside the rack. So i placed the sender /receiv outside. Ideas welcome... ;-)
 
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#2
As long as you use the resistors you shouldn't worry about voltage levels.
 
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#3
The Pi has certain overvoltage protection circuits for an input in place, but current for a single input line should be limited to less than 16mA, for the whole GPIO below 50mA, thus resistor design values do highly depend on the driving current capabilities of the corresponding output device's capabilities.

The main purpose to have a limiting resistor in place is to cater for the possibility that a GPIO line is switched to output mode and without a resistor you typically will shortcircuit the output driver port and destroy the output transistor.

A 1kOhm resistor will limit the current in either case to a max of 5mA for 5V operating voltage.

You can use voltage dividers, but you do need to know the driving current capabilities of the connected output driver ports, the input current requirements of the involved input ports, the voltage levels for high/low condition and design the resistor values accordingly (in theory you also do need to take the parasitic capacitance values into account as you charge/discharge them via passive resistors).
 
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#4
Very thanks!
So the overvoltage i´snt the major problem but the resulting current should be limited - right? For this, the 1kOhm is responsible in the wiring diagram...
 
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#5
What about the sender? I read multiple times that the range of the sender is much higher when used with 5V instead of 3.3V. So wouldn't it be a good idea to use a level shifter to drive the sender with 5V instead of the 3.3V provided by the GPIOs?
 
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#6
Hi...as per my knowledge limiting resistor in place is to cater for the possibility that a GPIO line is switched to output mode and without a resistor you typically will shortcircuit the output driver port and destroy the output transistor.

bittele electronics
 
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#7
Hi...RFM22 or RFM23 modules are available at 433MHz, much more capable and you get to choose channel, unique key, bandwidth v. range and they are bidirectional transceivers capable of automatic retry.  There are libraries available for driving them (SPI interface).  Line of sight 1km is possible if I recall some of my experiments.
 
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