Active low transmitter question

[LEDave]

Can someone kindly help please?

I have a RF Transmitter that transmits active low but to avoid 'floating voltages' (that could trigger a not wanted transmission) I was thinking the above cct might prevent this happening.

My thinking is the 10k resistor would hold the Transmitter input and pin3 on the Pic high until my code would make pin3 go low for a few milliseconds and make the Transmitter transmit, am I in the right ballpark with my thinking?

As ever all help very much appreciated.

[mpgmike]

I suppose it boils down to how much "oomph" the transmitter packs. If it's a weak signal, it may not be able to overcome the 10k pull-up. If it has sufficient amp capability, then you're golden. The best answer will be given from your test. It either works or it doesn't. As posted, not enough information to go on.

[LEDave]

Thanks for the reply mpgmike

Wouldn't making pin3 on the pic go low for say 50ms make the transmitter which transmits when 'active low' transmit as the Tx pin on the transmitter is on the same line as the pic pin3 set Output LOW 50ms in code?

[mpgmike]

WHAT??? Your transmitter is "Talking" and your PIC should be "Listening"; or receiving. In order for your PIC to receive/listen, your pin3 must be configured as a digital (ANSEL Register reads 0 for that pin) input (TRIS Register set to 1 for that pin). For you to have your PIC make that transmission line low, you have to clear the TRIS bit to make it an output, then use either the PORT or LAT Register to make the pin3 low.

WHAT DOES ANY OF THIS HAVE TO DO WITH RECEIVING A TRANSMISSION??!!?!?!??? What do you hope to accomplish??

[LEDave]

"WHAT DOES ANY OF THIS HAVE TO DO WITH RECEIVING A TRANSMISSION??!!?!?!??? What do you hope to accomplish??"

mpgmike - I've never mentioned or talked about 'RECEIVING A TRANSMISSION??!!?!?!???' Exactly the opposite. I'm asking if pin3 on the pic is pulled low in code, there will be a wire from pin3 on the pic to the Tx pin on the RF transmitter, the transmitter operates when the Tx pin goes low so I'm asking if I pull pin3 LOW for say 50ms that should make the transmitter transmit.

All I'm trying to do is replicate and replace a push button from the transmitter Tx pin to ground by using a pic to send the Tx line LOW. The 10k resistor being added to keep the line High to stop any floating voltage causing a 'false' transmit.

[mpgmike]

If your question is, "Can the PIC safely overcome the 10k pull-up resistor?", the answer is absolutely yes. Again, will it do what you want, you'll just have to try it and see.

[richard]

posting pictures of text is really annoying , post the actual data sheet or a link.

the annoying picture that cannot be seen when replying says that the output pins are set to reflect the incoming pkt data
why would the pins change between pkts ?
how can the pic even know when new data has arrived ?
how do u know when data is valid ?
there is no mention of pullups or pull downs in schematic
a pull down here would be nothing but detrimental in my view

[Ioannis]

Data sheet is needed for sure.

The module says 5V tolerant, so I guess it works on 3.3V maybe? In that case you better lower the 5V of the PIC to 3.3V just to be sure that no problems may come up.

Also the module will transmit when a change on input pins occurs. This means either when the switch is closed (grounding the input) or the switch is opened, leaving the input pin on the air.

So you will have two transmissions and this is how the receiver will reflect transmitters status.

Ioannis

P.S. By the way, do you get email notifications when there is a reply? I do not once again...

[richard]

So how does this look for basic a Tx test loop?

wont work like you think , it will tx twice once as pin goes low then again as it goes high

Telemetry mode - Transmit (TX)
GAMMA module configured as a transmitter
Operation: When configured as a transmitter the GAMMA module will automatically default to
low power sleep mode. A change on any input(s) will cause the GAMMA to wake, read all inputs
and initiate RF transmission, (multiple input changes may take place simultaneously).

data sheet

[LEDave]

http://www.rfsolutions.co.uk/downloa...S-GAMMA-12.pdf

Ioannis / Richard - Hopefully I've uploaded a link to the RF Module (PDF was too large to upload directly).

It looks like there are two versions [Supply voltage Standard version 1.8 - 3.6 *V] & [Supply voltage high Voltage version “R” 3.6 - 16 *V]

Will post again this evening.

Ioannis - No email notifications received.

[LEDave]

Ok - So the transmitter will always Tx twice, on a button press to ground, then open contacts (if using a button). Or a transition from HIGH to LOW to High if using a pic GPIO pin to cause a Tx, correct?

From the data sheet:

'When configured as transmitter: Pins 3, 4, 7, 8, 9, 11, 12, 13 Inputs are internally pulled high, active low'

So no pullup needed. How about if I set a TRIS bit to INPUT, corresponding GPIO pin left open but GPIO pin connected to Tx pin 3 say which is internally pulled HIGH, active low. Then when I want to TX, switch the TRIS bit to OUTPUT and pull the corresponding GPIO pin LOW then switch the TRIS bit to INPUT again mimicking a button press.

Barking mad or genius?

[richard]

Barking mad or genius?

not genius yet

Inputs are internally pulled high, active low'

not that i can see, there is no active low, a tx occurs on state change
if tx telemetry mode engaged

you need to explain what mode you are employing and what you are trying to achieve