Active low transmitter question

[LEDave]

if an input pin on the module distinguishes between a high impedance high and a low impedance high then
its not a normal LVCMOS/LVTTL logic input , the data sheet has not described such a capability.

no point guessing ---- consult the salesman ---- Will do later today if possible and get back.

Just to help me - Data sheet says:

Inputs are internally pulled high, active low

Ok - This is my understanding / misunderstanding of how these things work - Please tell me which of these statements is correct / incorrect so that I can learn.

A/ INPUTS are high impedance 'Z' state (floating)
B/ 'Z' state could be anywhere from High to Low unless pulled into a High/Low state via a resistor(10k)
C/ OUTPUTS are just High / Low

Data sheet for Transmitter says 'Input internally held high' (So an internal pullup resistor to +v) and then pulled low via push button or in my case a Pic, this will cause a Tx, Lora Mode 5 is the Tx default (720ms) not sure if I hold Tx Input pin low for this length of time, another question for the sales guy I guess.

[richard]

A/ INPUTS are high impedance 'Z' state (floating)

no, INPUTS are always high impedance , there is no "high Z" state for digital inputs and they should be pulled into a High/Low state via a resistor so as not to float if left unconnected and they are active

B/ 'Z' state could be anywhere from High to Low unless pulled into a High/Low state via a resistor(10k)

hmmm. high z is high z its not an output

C/ OUTPUTS are just High / Low

no outputs are what you could tristate (high z) to stop that pin from loading a shared bus inappropriately
otherwise they are just High / Low if loaded correctly.

Data sheet for Transmitter says 'Input internally held high' (So an internal pullup resistor to +v) and then pulled low via push button or in my case a Pic, this will cause a Tx, Lora Mode 5 is the Tx default (720ms) not sure if I hold Tx Input pin low for this length of time, another question for the sales guy I guess.

pure speculation , i believe the demo totally misleads by not specifying if the sw is push on / push off or momentary.
there is no mention of debouncing , rearming time or several other things

\

[LEDave]

Hi Richard / Everyone

OK - So I managed to get a call into the salesman today and he said:

First off the video. The module in the video is a Bravo module, very similar to the Gamma module (the ones I have) in fact they are the forerunner on my module but a difference is the video module (Bravo) has 'latching and momentary' outputs the video shows a momentary button press onto a latched output on the Rx, so that explains the Led staying on.

On to my module (Gamma). As I understand it now, these don't have latched outputs on the Rx. And the Tx / Rx cycle is this:

1/ The default module setting is for a 720ms Tx set on mode5.

2/ The Tx occurs when a Tx pin is pulled Low and must be held low for more than 720ms.

3/ If the Tx pin changes state (goes high) within the 720ms time frame, then the transmitter will automatically resend another two data packets*.

4/ The Tx cycle is: Tx pin is set Low - stays low for greater than 720ms - Tx pin goes High, ends Tx.

5/ The corresponding Rx pin would then go High for greater than 720ms - Then go Low again when the Tx pin goes High.

*Just as an aside, I really don't want false triggering on the Rx output pin as this will be attached to a pic input pin then output to a relay alarm buzzer.

Any way a little clearer I hope?

[LEDave]

As an aside. Has anyone used a 2N7000 Mosfet attached to a 3.3v pic output to drive a relay?

The schematic (link below) is exactly what I want to do from a pic output pin rather than the Receiver output pin.

http:///www.rfsolutions.co.uk/downlo...elayOutput.pdf

Any thoughts appreciated as ever.

Dave

[peterdeco1]

Never tried 2N7000 but for 3V outputs, we use an IRLZ44N. It's a power mosfet that we use to switch up to a couple of amps without needing a heatsink.

[LEDave]

Thanks for the reply peterdeco1 - So would that be the same wiring / resistor configuration as the 2N7000 (see link diagram) a straight swap in other words?

[peterdeco1]

Yes, although I use a 47K across gate to source. Either way it will work. EDIT Note there is a L in the part number for Logic Level. It is NOT the standard F.