Power supply. Serial data.

E

Emile

Senior Member
Hello everyone.

A question for you.

I recovered two 433 Mhz RF modules for wireless RS232 communication
between 2 picaxe.

There is a problem : I have seen on the RF module datasheet
" 1 serial port low (3.3V) Rx Tx Rts Cts "

The problem is that my picaxe is 5V and the RF module is 3.3 V ....
I wanted to know how to adjust the tension .

To use the serial RS232 3.3V with my picaxe (3.3 by transforming the 5v)
I am looking for a product (Maxim like MAX232) to convert 3.3 to 5 and 5 to 3.3 , I will use serin and serout to make bidirectionnel wireless RS232.

Thanks for your help !

Emile
 
E

eclectic

Moderator
Emile said:
Hello everyone.

A question for you.

I recovered two 433 Mhz RF modules for wireless RS232 communication
between 2 picaxe.

There is a problem : I have seen on the RF module datasheet
" 1 serial port low (3.3V) Rx Tx Rts Cts "

The problem is that my picaxe is 5V and the RF module is 3.3 V ....
I wanted to know how to adjust the tension .

To use the serial RS232 3.3V with my picaxe (3.3 by transforming the 5v)
I am looking for a product (Maxim like MAX232) to convert 3.3 to 5 and 5 to 3.3 , I will use serin and serout to make bidirectionnel wireless RS232.

Thanks for your help !

Emile
Click to expand...
Please post a link to the datasheet.
 
C

calvinsykes

Member
The problem is that my picaxe is 5V and the RF module is 3.3 V ....
Click to expand...
Any PICAXE ought to run on 3V (eg. 2AA cells). There are also low-voltage versions of some chips that are specially designed to work on 3V.
 
E

Emile

Senior Member
There is no other way to use the RS232 with my picaxe 20X2 ?

Max232 or other product like this ?

Thanks

Emile
 
C

calvinsykes

Member
The radio module wants 3.3V; your PICAXE 20X2 is running on 5V. It will run just as well on 3.3V (the same as the radio module). So you don't need any extra circuitry. What's the problem? :)
 
W

westaust55

Moderator
Some alternatives are:
. Use two resistors as a potential divider on the signal between the 5V Picaxe and the Tx module. Something like a 10k and 4.7k resistor with the 4.7k to the Picaxe pin. Then tap off at the junction of the two resistors to obtain a signal for the 3.3V Tx module.
For the Rx to Picaxe signal wire that without any components between.

2. Use a 2N7000 FET as a level shifter on each signal line. I have discussed this approach previously in posts on this forum.
 
hippy

hippy

Ex-Staff (retired)
Emile said:
There is no other way to use the RS232 with my picaxe 20X2 ?
Click to expand...
If the RF modules expect 3.3V then they are not RS232. Unless you areasking a different question you do not need any MAX2322 or similar to interface them to a PICAXE . The easiest option is to choose a PICAXE that can run at 3.3V.
 
E

Emile

Senior Member
Thanks for all your reply.

I think I will buy picaxe 28 X 2 with low voltage 3.3V.

The probleme is that i will make a bidirectionnal serial links. And use the serial RS232 of the HF module to communicate.


I have to send data to the HF module and receive data of the HF module , to receive no problems but to send ... 5 V will destruct the HM module.

I think that the easy answer is to use a low voltage picaxe. Or to use the Westaust method.

Thanks !

Emile
 
Last edited:
W

westaust55

Moderator
@Emile,

When you say: “i will make a bidirectional serial links”

Do you mean:
- a single wire with bi-directional data flow, or
- separate wires for Tx (SEROUT) and Rx (SERIN) signals between the RF module and the PICAXE.


The use of a 2N7000 FET in the signal line(s) has been done successfully for
i2c comms and does provide a bidirectional link. The concept was developed
and published in a technical paper by Philips (now NXP)


Have a read of this thread:
http://www.picaxeforum.co.uk/showthread.php?t=13347
and post 4 here:
http://www.picaxeforum.co.uk/showthread.php?t=14265
 
Last edited:
E

Emile

Senior Member
Hi Westaust,

I say :

- separate wires for Tx (SEROUT) and Rx (SERIN) signals between the RF module and the PICAXE.

Emile.
 
W

westaust55

Moderator
Yes, a PICAXE operating at 3 V will also work fine.


Earlier X2 parts were in seaprate 3V and 5V variants.

The very latest X2 parts as a single part will down to 3V (no separate 3V and 5V parts)
 
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