TX module heating up ????

[Megahertz]

Hi, I have a normal cheap chinese type TX module connected to my 877A.
PIC is looped to send an HSEROUT .....every 2 seconds.
Though it works but but my TX module is heating up for some reason, Anyone knows why this could be happening, data is going to the TX module via 10K already, should the resistance be changed?

[Jumper]

Maybe you have a 3.3V TX module and run it on 5V... if you connect an mA-meter you can see the consumption and check against the datasheet

[Megahertz]

Maybe you have a 3.3V TX module and run it on 5V... if you connect an mA-meter you can see the consumption and check against the datasheet

It is a 12V module, I am using the same for other 12V running applications as well. It is running smooth there.
I just wanted to confirm that using HSEROUT.... is not playing any part is heating up the module, may be data goes differently or something. I am sorry but my knowledge on the subject is limited so I am trying to erase the possibility of this thing.

Have you used such module with the above statements, could there be any connection in between ?

[mackrackit]

Serial data is serial data. Does not matter if it is generated by hardware or software.

Maybe it is a bad module? Have you tried swapping in another one?

[Megahertz]

Module is heating up because the data pin is high (around 4V) permanently and voltage fluctuates when data is there.
Is it normal when using HSEROUT, is it possible to make the data pin low in standby condition?

[Bruce]

The USART TX pin idles high, so a simple inverter circuit should be all you need to hold the RF transmitters data in pin low during idle periods.

[mackrackit]

The USART TX pin idles high, so a simple inverter circuit should be all you need to hold the RF transmitters data in pin low during idle periods.

Attachment 4465

Then an inverter will be needed on the receiver side also ???

I still think since you are basically building a transceiver you will want a way to turn the transmitter off when not in use. Does the module have an enable pin?

[Bruce]

Then an inverter will be needed on the receiver side also ???

Yes. The same circuit would be needed at the receiving end as well. Assuming the receivers data output idles low, which most do, then it holds the receiving PICs USART data input pin at logic 1, which is the idle input logic for the USART RX pin.

I still think since you are basically building a transceiver you will want a way to turn the transmitter off when not in use. Does the module have an enable pin?

If he's trying to build a transceiver using separate TX/RX modules on both ends, for sure. If you don't shut down the local receiver when transmitting, it takes longer for the receivers front-end to settle & recover from the strong local signal.

[Megahertz]

The USART TX pin idles high, so a simple inverter circuit should be all you need to hold the RF transmitters data in pin low during idle periods.

Attachment 4465

Bruce, is it possible you can draw me a quick circuit I can use on Rx side as well. I have C8050 & C8550, one of them is PNP & the other is NPN, which I can imagine could be used for the above purposes.
My Rx does stay Idle LOW and when data comes the voltage goes high on the data pin. Thanks

[mackrackit]

Mr Google gave this
http://dave.fraildream.net/micro/periph/232-ttl.html
but it is not me.

[Bruce]

The same circuit I already drew-up for you works on both ends. Your RF receiver data output pin would connect to the base of the PNP transistor labeled USART, and the PIC USART RX input pin would connect to the PNP collector/resistor node labeled RF TX.

The logic on the PIC USART RX input pin should idle high. With the RF receiver output idling LOW, that's exactly what you'll have on the PIC USART RX input with this same PNP inverter circuit.

It's just basic electronics...

[Megahertz]

I am sorry , I am on a very steep learning curve here. Just want to confirm that if there is any resistance needed between base and USART or direct connection is fine? Thanks

[Bruce]

You can get by without the base resistor. If you will be flipping power on/off a lot, and want to make sure the transistor stays off until it's turned on, you can use an inverter circuit like this one http://www.rentron.com/IRTORF_TX.gif

The 10K pull-up holds the base at logic 1 keeping the transistor off while the PIC powers up. If it's battery operated a small FET would be a better choice than a transistor.

I drew another quick schematic for you. Either receiver inverter will work, but the NPN circuit would be best.