Help with TX RX Temp Unit Please

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acestu
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Help with TX RX Temp Unit Please

Post by acestu »

Hi,

I was wondering if anybody had any info, circuit diagrams etc. on the following project that I am undertaking please:

Basically I want to build a road temperature sensor for my car using 433MHZ TX RX modules, ie a radio temperature sender that would sit under the bonnet near to the road, and an LCD receiver that could sit on the dash and be powered by the cigarette lighter socket, giving the road temp and perhaps an extra flashing warning sign when the temp gets to say 4 degrees. Any ideas, info, suggestions welcome.

Thanks In Advance
Acestu :)
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Hi
Are you going to use the 433MHz Tx Rx modules whose pin-out is as follows..
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Hi Stuart,

AS I know from the PM, you are going to use HT12E Encoder and HT12D Decoder IC for encoding and decoding the data. I think it will be good if you can play first with this two ICs using the diagram attached.
TX_RX.PNG
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Tx:
Here, I have used four switches S1, S2, S3 and S4 to give 4-bit parallel data (D0-D3). Since the switches are in active low state (i.e. low signal is sent when the switch is pressed), we need to add external pull-up resistors as shown, so as to provide a high signal by default. A resistance as high as 1Mohm is required in between OSC1 and OSC2 pins. The Transmitter Enable (TE, pin 14) pin is an active low pin. Thus, it is permanently grounded, so as to enable the transistor always. The output serial data DOUT is fed to the decoder module's DIN input directly.
The most important thing lies in the address pins (A0-A7, pin1-8). Suppose you have two wireless devices (A and B) in your house, both have different remote controls (AA and BB) and both implement the same type of RF module (say 433 MHz). AA is the remote control of A and BB is of B. Now, you obviously wouldn’t want AA to control B (which is the most probable case since both the devices use same kind of RF module, having same frequency!). This is where address pins come into play. There are 8 address pins, thus giving you an opportunity to have 8! (8 factorial) different and independent ways to connect to a device, so that there is no interference. The address pins MUST have the same address in both transmitter and receiver, or else the data won’t be transferred.
Rx:
The circuit of the receiver is also quite simple. Capacitor C1 is used between Vcc and GND for noise filtering. Apart from that, all the address pins (A0-A7, pin 1-8) are grounded, just as in transmitter. This is to ensure that the transmitted data is being received. Both the transmitter and the receiver MUST have the same address pins configuration. Pin 17 (VT) is enabled whenever the receiver receives any data. The serial data received is directly fed to pin 14 (DIN), which is then converted into 4-bit parallel data (D0-D3). A 33 kohm resistor is connected in between OSC1 and OSC2.
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Yes that's great Enamul, I will start setting that circuit up on my breadboard, I am enclosing a pic of my 433mhz kit, if it will not do I will get some like yours.

thanks
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433mhz_set.jpg
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

You can order pair while playing with existing...
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Hi Enamul,

I already have 2 sets of the 433mhz transmitter and receivers as in my pic, they are the same as the ones in the link that you sent me, I have had a look on ebay but I can't find any that have 8 pins on the receiver ?

thanks
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Don't worry..I have exactly same 2 pairs of the following one as well...
http://www.ebay.co.uk/itm/433Mhz-RF-tra ... 0781136559

Here is the link for those I have shown..
http://www.picaxe.com/Hardware/Add-on-M ... iver-Pair/
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Hi Enamul,

Sorry do I just have to order one pair from picaxe @ £9.99 ? , if so I will order it now.....

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Re: Help with TX RX Temp Unit Please

Post by Enamul »

I think we can start working with the existing pair..if face any difficulty we can go for PICAXE. Don't need now.
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Hi Enamul,

I am just checking, in the diagram there are 2 different voltages for Decoder & Encoder ie 9 volts and 5 volts, is this correct or could I run both of them on a 5v
regulated power supply ?

thanks
Acestu


EDIT:
I have a 1 Meg resister in the Encoder because that is all I have, what should I have in the Decoder side ?, I beleive it should be 50 times smaller...

ie 1 million divided by 50 = 20k

would I be right in thinking that if you put an 8 way dip switch on both encoder and decoder address ports then if they were set the same this would discriminate between same devices ?
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

in the diagram there are 2 different voltages for Decoder & Encoder ie 9 volts and 5 volts, is this correct or could I run both of them on a 5v regulated power supply ?
you can try with 5v for each unit..it should work.

I am not clear about oscillator resistor what you are asking...are you want to use 1 Mohm or not?
would I be right in thinking that if you put an 8 way dip switch on both encoder and decoder address ports then if they were set the same this would discriminate between same devices ?
8 way dip switch is fine to illustrate the behavior of address difference between encoder and decoder
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Hi Enamul,

Yes basically I have some 1.1 meg resisters coming from america and I only have 1 meg resister, so if I use this will I have to change the decoder resister ?

thanks
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Here is the graph...
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HT12E.png
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Yes basically I have some 1.1 meg resisters coming from america and I only have 1 meg resister, so if I use this will I have to change the decoder resister ?
The resistor in the circuit is 1Mohm not 1.1 Mohm..
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Resistor selection graph for HT12D..
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Here is the components for 5V system..
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Hi Enamul,

I have everything set up as per the diagram then, 9 volt battery on the encoder and 5 volt supply on the decoder, but it does not work for some reason,

Transmit Enable is grounded on encoder, I am enclosing a picture

thanks
Acestu
Decoder_Encoder.jpg
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Resistor R1(1.1M) is connected between oscillator pins (Osc1 & Osc2) to set transmitter frequency = 50×Receiver Frequency.
This is mentioned in some of the online tutorial..are you asking me that?

For 5V, Tx has Rosc=1 Mohm which sets Tx frequency to 3KHz and 5V power supply and Rosc=51 Kohm at Rx causes Rx frequeency to 150 KHz which satisfies that relation. Although this is not mentioned in data sheet or I might have missed that.
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

What are the resistors you are trying in Encoder and Decoders?
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Hi Enamul,
From the diagrams I assume that the supply voltage and the osc resister are selected from the graph (rosc), I have a 9 volt battery connected and a 1 meg resister
so it is wrong and should be a 1.1 meg which I have not got, I have ordered some but I don't think they will be here for a while as they are coming from America.

If the resisters are of the wrong value, will the LED's just not light up ?


thanks
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Re: Help with TX RX Temp Unit Please

Post by acestu »

1 Meg & 33k

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Re: Help with TX RX Temp Unit Please

Post by Enamul »

Can you please try with 47K resistor in place 33K?
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

If the resisters are of the wrong value, will the LED's just not light up ?
No if data is not transmitted..the LED will not turn ON
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Re: Help with TX RX Temp Unit Please

Post by acestu »

Hi Enamul,

I can't find a 47k resistor anywhere, I have tried with a 47k rotary pot but still not working.

thanks
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Re: Help with TX RX Temp Unit Please

Post by Enamul »

I have ordered mine pair couple of days back..they are on the way. I will let you know.
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