ZoneMikel's Blog

Brief Description

My purpose was to test this transmitter/receiver pair to see how far i could go and still reliably transmit data. I used my protoboard to transmit. The reciever was attached to a uart to rs232 converter then to the db9 port on my computer and i watched the input from hyperterminal.

Equipment

• ProtoBoard
• rct-433-as transmitter Mouser Part # 509-RCT-433-AS
• rcr-433 reciever Mouser Part #509-RCR-433-RPR
• A transistor and some 10K resistors for Conversion
• A few 4.7uF and .01uF Filter Capacitors
  

Prelab

Get and study data sheets for the transmitter and reciever. Brush up on rs-232 and ttl signaling levels.

Procedure

The first thing i did was get the Conversion circuit working. I’ve found that the other circuit i have listed does not work well with the 2N3904/6 transistors that i have on hand. I was only able to get the uart to rs232 portion to work, as soon as i plugged in the capacitor or the line going to rs-232 RX the circuit would stop working. So I only hooked up half of the ciruit using a 2N3906 and three 10K resistors. You can do that or use the other one way circuit. You should be comfortable enough with the signalling levels by this point to do this easily, if not i suggest you go back to those sections.

After thats hooked up connect it to the tx pin on the pic to make sure its transmitting correctly. Then hook up the reciever and put the data out line where your pic was connected (before the 10K going into the base of the transistor). You can get the data sheets for the reciever and transmitter in the links that i posted above in the equipment bullets. Hooking up the reciever is really simple, its just ground and power lines and a data out. I hook up all the ground and power lines just to be sure, and when in doubt remember vsS = “sink” so its the ground.

I hooked the transmitter into my “protoboard”.

There is a program on the pic that just transmits a number like 10 times and then does a newline. That way i can print out lots of data and see what number it messed up on. I used the lowest setting i could for the pic, since it has a 20Mhz clock i can use any baud rate slower than 1200.

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#include <16F877.h>
#device adc=8
#use delay(clock=20000000)
#fuses NOWDT,HS,NOPUT,NOLVP
#use rs232(baud=1200,parity=E,xmit=PIN_C6,rcv=PIN_C7,bits=8)
int i =0;
int j=0;
void main()
{
   setup_adc_ports(NO_ANALOGS);
   setup_adc(ADC_OFF);
   setup_psp(PSP_DISABLED);
   setup_spi(FALSE);
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DISABLED,0,1);
 
   output_b(0xFF);
 
   printf("\f \f \f \r \f \f \f \r \f \f \f \r");
   printf("Start");
   while(1){
      for (j=0;j<10;j++){
      printf(".%i",i);
      }
      printf("\r\n");
      i++;
 
   }
 
}

Filter Capacitors
In the datasheet for both the transmitter and reciver it says you should use a “bypass” and “filter” cap. I noticed a great improvement of signal quality when i installed these. Pretty much for both of them i just connected them between ground and power in close proximity to the chip, I did this on both the tx and rx ends. You should be able to make it out from the pictures.

Antenna
There is some weird calculation to get “1/4″ of the wave or soemthing like that to calculate the optimum lenght of the antenna. Other people calculated it to 17cm. POST LINK HERE So, I just used a 17cm peice of telephone wire.

Conclusions

The pair works pretty good going at 1200 baud, I was able to transmit through walls. I transmitted at least 20 feet away through walls without loosing any info. This was only after installing the filter capacitors though.

In the datasheets it recommends that you invert the output signal on both ends. This allows you to only transmit when you are actually transmitting, if you dont do this to hold the line without sending data you have to send a ‘1′, but if you invert before it hits the transmitter and then invert coming out of the reciever then you wont need to waste power. If you are transmitting from the pic then you need to set the INVERT option in your program, or you can just invert after that. I didnt implement this part but i might later on.

When you are not transmitting the reciever picks up some weird square wave that does strange things. Then, when you start to transmit some of this weird square wave is picked up in the beggining of your signal, this almost always makes the first part of a string of data get garbled. You can get around this by just constantly transmitting data, which might not be efficent. Possibly you could create some kind of circuit to filter this out, or maybe by inverting the singal it would help ? Just something to consider.

Depending on the needed applications of this it seems to be a very nice way to transmit data, I plan on making a RC car, for that it should work just fine.

1. nazeer says:

   February 22, 2010 at 1:51 am

   what is full form of RCT word and what AS indicates
2. admin says:

   March 28, 2010 at 12:18 am

   Sorry the pictures were lost !