RF Wireless door bell

[muraku]

Hello Chris,

My hobby is electronics and I am an IT professional working for Siemens. Just now I saw your project on: "Simple RF Receiver And Transmitter @ 27 MHz" and the clear explanation there made me speech less. In fact I was looking for something neat and clear as yours here for quite sometime. Thank you very much for all the effort you have made.

Now, let me explain my objective for searching such a neat and clear project on RF receiver. I wish to make a wireless doorbell myself with a range of about 50 meters just like the Chinese made wireless doorbells (please refer to the below URL):

http://yume-deals.blogspot.in/2012/10/t ... -just.html

Now, while surfing the internet for this, I came across another website: (http://www.talkingelectronics.com/te_in ... index.html) that explains how to build one such with an operating frequency of about 303 MHz and which will use an in-built antenna. I was successful in making the transmitter part but could not make the receiver part. I had also purchased a ready made Chinese doorbell and could tune my home made transmitter unit with it nicely.

Looking at your 27 MHz project, I would request you to present another project which will help your readers to make a 303 MHz Wireless Doorbell easily at home with a range of about 50 meters with a built-in antenna. Last but not the least, the beauty of the Chinese doorbell is that the receiver unit runs from just 3 volts battery and consumes 6 micro ampere current when idle!!

Though electronics is my hobby but I could not afford an oscilloscope to my workbench as yet . However, I do possess a portable frequency counter:
GY 560. Please also let me know if this will help me to test the receiver circuit.

Waiting eagerly for your response.

Thank you again for the wonderful project and your time to read this long e-mail of mine.
Kind regards,
Raj Kumar Mukherji

[ThePyroElectro]

Hi Muraku,

Thank you for stopping by! We actually do have this exact project in mind, although it will not differ very much from the 27 MHz transmitter/receiver project.

The advantage to bumping up to 303 MHz or 434 MHz (two common legally available frequencies in the USA) is that you can actually fit the antenna onto your PCB and the transmission will be able to travel further, 50 meters is definitely do-able. My guess about your receiver is that your tuning tank circuit L+C is not set for 303 MHz correctly, or that additional capacitance has crept into your system messing up the tank circuit. Do you happen to have any photos of your transmitter/receiver that you can share?

This project is on our list to get done, but we have so many things being done currently, it might take a month or two before we can get a proper article written about this topic.

[muraku]

Hi there,

Thank you very much for the response.

In fact your response in a way motivated me to the extent that I have atleast got a friend by my side who is also trying to make the same project as mine. I was searching the internet for some sort of help on this from some one for the past 6 months or so and believe me this is the first ever positive & prompt response which I have received.

Anyways, as far as my Rx and Tx circuits are concerned, I will upload them soon for you to check.

Take care.

Regards,
Raj

[muraku]

Hi Chris,

Please find the pictures of the 303MHz Receiver and Transmitter which I have made, in the following URL. I have also attached 2 images of the schematic of the Rx. They have to be added up together in order to view as one complete image (please add A_Schematic + B_Schematic).

http://www.use.com/UHF_Rx_Tx_ba0b9f47d20968c75cc4

I want to remind you that my Tx is working fine and I have followed the same circuit as the URL mentioned below:

http://www.google.co.in/imgres?imgurl=h ... m=1&itbs=1

However, as far as the Rx is concerned, I am using the one which is used in the Chinese door bell. The only differences in my Rx circuit are:

a. All resistors are 1/4 watt instead of 1/8 watt which are used in the Chinese door bell since 1/8 watt resistors are not available here
b. The C5 in Rx is 4.7pF instead of 4pF used in the original doorbell circuit

The tank circuit comprising of C1+L2 uses 8pF and 1.5 turns, 3.5mm/4mm diameter air coil in the actual doorbell circuit. However, since I could not determine the exact SWG of the wire, I tried using 21, 22 and 24 SWG respectively, keeping C1 to 8pF. However, none of the combinations did work. Last thing I tried was a 3mm, 24 SWG with 2.5 turns coil, but that also did not work. By the way, I am trying to match the frequency of my Tx-Rx by adjusting the variable capacitor of the Tx. The PCB of my Rx is hand made as you can see and it is a 2x2 inch PCB.

I have not yet attached the bell circuit to my Rx. However, using a RED LED at the Collector of Q6 to test the output. Rest of all the component values of the Rx circuit are exactly the same as that of the original doorbell receiver circuit. I have done this deliberately to find out the effect of the sensitivity & performance of my Rx as compared to the actual circuit since the size of the PCB is little bigger than the actual one.

Please let me know if you need any further information and also check if there is anything wrong in my schematic since I have referenced the original Chinese doorbell Rx PCB to draw the it.

Waiting for your response.

Regards,
Raj

[muraku]

Hi,

Did you figure out anything with what I had provided in my last reply?

Regards,
Raj [muraku]

[ThePyroElectro]

Hi Chris,

Please find the pictures of the 303MHz Receiver and Transmitter which I have made, in the following URL. I have also attached 2 images of the schematic of the Rx. They have to be added up together in order to view as one complete image (please add A_Schematic + B_Schematic).

...
...
...

Please let me know if you need any further information and also check if there is anything wrong in my schematic since I have referenced the original Chinese doorbell Rx PCB to draw the it.

Waiting for your response.

Regards,
Raj

Hi Raj,

I didn't see anything out of the ordinary with your receiver circuit. But I'm still willing to bet the difficulty is in your tank circuit.

Did you attempt any debug to see the signals coming through your circuit, either through oscilloscope or spectrum analyzer? A spectrum analysis through your receiver's front end would tell you whether you have things tuned for the right frequency or not.

I'm still hoping to get a proper set of articles written for a project like what you're trying to build. Hopefully I can get it done by next month....we'll see.

[muraku]

Hi there,

Good morning.

Thank you for your time to go through my circuits and for the relevant suggestions.

Well, I also have the same feeling about the Tank circuit. The thought of checking the circuit with an oscilloscope came to my mind the very moment when I found it not responding to the transmitter. However, I could not manage one. Then I thought of using one of the several free downloadable PC sound card oscilloscopes for my need. So, I installed the Soundcard Oscilloscope by Christian Zeitnitz and the Zelescope oscilloscope and spectrum analyzer respectively on my PC. However, the max frequency limit was found to be in some KHz range as far as the Soundcard Oscilloscope is concerned while the oscillator stage of the receiver should produce something around 300 MHz plus and therefore the software was removed from my computer.

I could not faithfully use the Zelescope due to the reason that I did not find a suitable hand made probe for it to connect to the sound card of my PC. Any suggestions for that will be great.

I am glad to know that you are hoping to present one such circuit by the next month and I'm eagerly waiting for that.

Regards,
Raj

[muraku]

Hi Chris,

This is a follow up to check if you have got hold of an article on wireless doorbell as yet & your future plan about it. I would also request you to suggest me a spectrum analyzer software (along with some probe details to safely connect to the sound card of my PC)which will help me to check the tank circuit oscillation of my Rx unit.

Thank you,
Regards,
Raj

[ThePyroElectro]

Hi Chris,

This is a follow up to check if you have got hold of an article on wireless doorbell as yet & your future plan about it. I would also request you to suggest me a spectrum analyzer software (along with some probe details to safely connect to the sound card of my PC)which will help me to check the tank circuit oscillation of my Rx unit.

Thank you,
Regards,
Raj

Hi Muraku,

You won't find any useful spectrum analyzer software for sound card. A sound card A-to-D is limited at around 22 KHz. To check higher frequency 434 MHz you would need a real spectrum analyzer (for example: Agilent MXA, R&S FSL). There are probably some cheap spectrum analyzers made-in-china on ebay.

Also, the probe will probably mess up the tank circuit's oscillations if you touch it. But if you can get your hands on a real spectrum analyzer (R&S/Agilent), I've found that the tank circuit oscillations are powerful enough that a good quality spectrum analyzer can pick up the oscillation without even touching the circuit.

Anyway, I'm busy working on finishing off our second course on PyroEDU, An Introduction To Digital Electronics, when I finish that I'll start working on building this project. Although my transmitter will differ from yours because I want to use a 434 MHz oscillator. Until then!

[muraku]

Hi Chris,

I am ok with 434 MHz. However, my only request to you is not to use the 434 MHZ transmitter & receiver modules that are commonly available in the market. Because, that will hardly give us any scope in constructing the Tx & Rx and understanding the design and working principle of the same. Other than that we also have to ensure that the Tx should run from a 9 Volt battery while the Rx should not use over 3 to 4.5 Volts battery.

Looking forward to the project from you.

Regards,
Muraku

[ThePyroElectro]

Hi Chris,

I am ok with 434 MHz. However, my only request to you is not to use the 434 MHZ transmitter & receiver modules that are commonly available in the market. Because, that will hardly give us any scope in constructing the Tx & Rx and understanding the design and working principle of the same. Other than that we also have to ensure that the Tx should run from a 9 Volt battery while the Rx should not use over 3 to 4.5 Volts battery.

Looking forward to the project from you.

Regards,
Muraku

Haha, that would be cheating! You have to build it yourself from the components up!

Give me 1-2 weeks and I will show you the schematic that I come up with for transmitter and receiver.

[muraku]

Hi there,

Hope you are fine.

Have you already started working on the project? When can I expect it published here?

Regards,
Raj

[ThePyroElectro]

Hi there,

Hope you are fine.

Have you already started working on the project? When can I expect it published here?

Regards,
Raj

Hi Raj,

We're currently rolling out PyroEDU's 2nd course: An Introduction To Digital Electronics so I'm low on time at the moment.

I had a little while to spend on this project last weekend and I decided on the transmitter method/circuitry that I want to use. A really easy way to make a high frequency transmitter (315 MHz or 434 MHz) is with a SAW resonantor:


RO2073: http://www.rfm.com/products/spec_sheet.php?record=RO2073
Datasheet: http://www.rfm.com/products/data/ro2073.pdf

Without any amplification and only basic filtering you can use these guys to transmit some output at the specific center frequency and minimal components. However, I do have my doubts that this transmitter would work up to 50 meters. Without some additional amplification either at the transmitter end or the receiver end....but we'll see as I continue with the design.

I'm hoping to get some time this coming weekend so I can work on the receiver design, which I know you're more interested in seeing.

Slowly I'll get there, hopefully you don't lose interest by then ....we're just really busy, but we'll get there!

[muraku]

Hi Chris,

Thank you for replying back.

I have seen transmitter circuit and the datasheet of the SAW resonator. However, you are correct in your assumption that I am mostly interested in the receiver part.

As far as the components are concerned that are used in the SAW resonator circuit, they have used a NPN transistor MPS-H10 and this type of component is not available in the Indian market. Hence, I would request you to use the parts in the receiver circuit which are universally available. So that it will also help other readers who might be interested in building the project.

Waiting for the receiver from you.

Regards,
Raj

[muraku]

Hi Chris,

Well, after the final release of your Intro to Digital Electronics, I hope you have now started concentrating on my proposed project. May I therefore start the "count down"?

Thanks,
Raj