Hello guys,

I would like some help with the circuit attached. First of all let me explain you the purpose of the circuit.
I am trying to build a wireless (433 MHz) pir sensor. The pir sensor is connected to the transmitter and when motion is detected, the signal is firstly encoded through the IC HT12E and then transmitted to the receiver. The transmitter is necessary to be battery operated this is why I use the transistor Q6. The problem is that the decoder in the other side (HT12D) is latching type. Therefore, in the transmitter side, when the pir detects motion, both transistors Q5 and Q6 turn on and AD8 of HT12E goes to ground. In order to get rid of the "problem of latching behaviour" of the receiver, it is necessary, at first place to turn off the transistor Q5 (invert the transmitted signal) and then stop the circuit power supply (to be able to use battery for long time). Do you have any idea why this circuit does not work as I expect?

Thank you in advance. I wish everyone to be healthy these difficult days!

 

hi Pan,
Welcome to AAC.
Why do want to encode the PIR output before transmission.?
Most PIR's output a +3V DC level when activated.
E

 

 

PIR = Pyroelectric Infrared Receiver?, Periodic Impulse Radar?

 

hi Pan,
Welcome to AAC.
Why do want to encode the PIR output before transmission.?
Most PIR's output a +3V DC level when activated.
E

Hi Eric,

First of all thank you for your answer. Is there any other way to transmit data through 433Mhz modules without a microcontroller? I plan to use 4 battery operated transmitters and one receiver (off course only one transmitter will be active per time).

 

PIR = Pyroelectric Infrared Receiver?, Periodic Impulse Radar?

Infrared

 

I tested the circuit with bigger capacitor and it really works! The value I used is 3300 μF.

 

Hi Pan,
Can you confirm what the actual signal output is from the PIR Passive Infra Red sensor, usually 0v+3V or have you got an encoded type.?
E

 

hi Pan,
Welcome to AAC.
Why do want to encode the PIR output before transmission.?
Most PIR's output a +3V DC level when activated.
E

The 433 MHz receivers get tons of false triggers all the time. You need encoding to distinguish the signal from noise.

Bob

 

Hi Pan,
Can you confirm what the actual signal output is from the PIR Passive Infra Red sensor, usually 0v+3V or have you got an encoded type.?
E

The signal output of the PIR Sensor is 1.3V

 

hi Bob,
If I understand correctly, the TS plans to use an encoder chip at the TX and he is only using one 'signal' state Passive /Active.
There are many ways to modulate a single state.
E

 

Hi Pan
The signal output of the PIR Sensor is 1.3V
I assume that is 0V inactive and +1.3V DC during the activated period.??
E

 

Hi Pan
The signal output of the PIR Sensor is 1.3V
I assume that is 0V inactive and +1.3V DC during the activated period.??
E

Yes Eric exactly!

 

hi,
I would consider using the 1.3V to enable a low power, low frequency oscillator, which would modulate the RF carrier of the 433MHz TX.
The enable signal signal would also power up the TX module.

At the RX end a simple signal demodulator could be used to enable an alarm or some other device.

No encoding IC's required.

E


Update:
Check this video.

 

hi,
I would consider using the 1.3V to enable a low power, low frequency oscillator, which would modulate the RF carrier of the 433MHz TX.
The enable signal signal would also power up the TX module.

At the RX end a simple signal demodulator could be used to enable an alarm or some other device.

No encoding IC's required.

E


Update:
Check this video.

Thank you Eric, I understand what you mean, and this circuit fine for a single signal. But as I wrote earlier, I need four transmitters sending to one receiver. How can I distinguish, at the receiver side, which was the transmitter that sent the signal? In any case thank you all for your answers.

 

hi Pan,
I had based my suggestions on your first post, ie: a single TX.
What at the receiving end of the project are the 4,TX signals going to be used for.?

I was thinking tone modulation would be a solution.??

E

 

The 433 Mhz modules he is using are not modulated. The input turns the carrier on or off, I know, I have used them. They only work reliably if you send and check for a specific bit pattern(s).

Bob

 

hi Bob,
If they are same model as the types I use, they will accept a low frequency modulation signal.
Some apps use a sqr wave tone from 500Hz to 1500Hz , the frequency proportional to a signal input voltage.
The RX demodulator set for 500Hx thru 1500Hz will produce a voltage proportional to frequency,

I am not suggesting that it would suitable for the TS 4 off TX remotes into one RX, I would use a TX encoder and a decoder IC or a Nano at the RX end.

E

 

Yes, you could do that, but the power usage would be pretty high if the signal had to be modulated all the time.

Bob

 

I am not sure why the constraint is this particular transmitter. There are readily available 4-channel receivers that learn separate uniquely encoded transmitters, no external encoding/decoding needed.