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scottnj

I need help with a transmitter

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I have a 4 button remote control. I want to incorporate this functionality into my own project. The main IC is a MC145026D, which I have found the datasheet for.

I can get the same IC (dip, not surface mount).

Then I guess I need to match the clock rate.

I also need to find out what frequency this transmits at, then I can just find a transmitter module that matches.

How can I figure out what frequency this transmits at?
What is the clock rate?
What are the other surface mounted components?
They are:

  • blue with numbers
  • black with numbers
  • light brown with what looks like Y0
  • brown
  • silver

post-9753-14279142341275_thumb.jpg

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Guest Alun

I have a 4 button remote control. I want to incorporate this functionality into my own project. The main IC is a MC145026D, which I have found the datasheet for.

So I'm assuming you want to reverse engineer this circuit which will be quite hard to do, but how about the reciever?

The RF of the circuit will need to be exactly the same layout as the module in order for it to work properly, forget about using vero board - it simply won't work and you might need to used surface mount componants for it to work.

I can get the same IC (dip, not surface mount).
Then I guess I need to match the clock rate.

I also need to find out what frequency this transmits at, then I can just find a transmitter module that matches.


Wait, is this circuit a transmitter or a reciever?  It looks like a transmitter to me, but you've asked for a transmitter module that matches it ??? is this just a typo didn't you mean you need a reciever module?

How can I figure out what frequency this transmits at?
What is the clock rate?

With a frequency counter.

A scanner could be used to deturmine the RF frequency but I guess it's between 300MHz and 1GHz  may be even hight but it'll probably be about 433MHz.

What are the other surface mounted components?
They are:
  • blue with numbers
  • black with numbers
  • light brown with what looks like Y0
  • brown
  • silver




Small surface mount capacitors and three legged devices are often unmarked so I'll do my best for you.

Transistors: ?1, ?3, RA4E
RF Transistor: 3E
I can't tell whether the transistors are bipolar, NPN, PNP MOSFET or JUGFET - but you can conduct tests on them and reverse engineer the circuit more by looking at the connections and if you're experianced enough you might be able to guess.

Surface mount resistors are marked with their value followed by the number of zeros on the end:
154: 150k resistor
623: 6k2 resistor
181: 180R resistor
104: 100K resistor
1002: 10K presision resistor
The tollerance of the reisitors is normally 1% for units marked with 3 numbers and 0.1% for those with 4 numbers.

Capacitors - as they're unmarked I'll try to guess their approximate values from the layout but I strongly recommend you measure them removed from the circuit with a capacitance meter.
?2, ?4 about 100nf decoupling capacitors - not criticle
?5 - no idea.
?6 - 1pf to 10pf - likely to be a RF bypass capacitor on the RF oscillator.
Y0 - 1pf to 33pf - possibly a part of the tuned circuit and will depend on the frequency.


I forgot to mention, I do not have an oscilloscope.

Good luck, this is hard enough to do anyway but you'll need a lot of luck if you don't have a very good oscillosope.

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I found the manufacturer of the transmitter on the web.
The spec sheet has the following info
http://www.touchtronics.com/images/p814-n2.pdf

814 Receiver:

FCC Approved
RF System 6561 Digital Codes
Voltage 12 Volt DC (available in 24 Volt DC)
Output 300mA
Frequency 303 MHz
Range 60 Feet (typical - using standard 36” grey, wire style, antenna)
Note: Range may be extended with an externally mounted antenna

814 Transmitter:

FCC Approved
RF System 6561 Digital Codes
Battery 12 Volt DC
Cycles 32,400 One Second Pulses
Frequency 303 MHz


So the transmitter transmits at 303MHz. After a quick search on google I found this
http://www.computronics.com.au/module/txrxpair/txrx_data.pdf
which will transmit at 303.875MHz.

I am new to RF, should something like this work?

I am guessing "Cycles = 32,400 One Second Pulses" is a typo, maybe they mean 32400 pulses/second?

The 16 pin IC is just an encoder. It sends the addresses and sata out in serial. The data sheet is here
http://www.freescale.com/files/rf_if/doc/data_sheet/MC145026.pdf
On page 10 they have the equation for the frequency, which is set by Rtc, Ctc, and Rs.

What do you think the target frequency should be, 32.4KHz, or some mutiple of 32.4k?

Am I over simplifing this?

Strange that the blue resistors are precision, they appear to just be pull ups for the logic of the 2 data Pins.

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Guest Alun

I think 32,400 1 second pulses is refuring to the battery life, and the 300mA output on the reciever is the maximum load you can connect to it, RF output is always measured in watts, never in current.

My advice to you is to buy a reciever for the transmitter module or failing that buy a matched transmitter and reciever, you might be able to revverse engineer this but I don't think it's worth the effort.

I don't know about the precision resistors, they might be part of an oscillator or something, I just assumed they're precision because they have 4 numbers on them. Precision resistors always have more numbers because they are more acurate and there'd be no point in specifying a 1% tollerance resistor to a value with significant figures greater than 1/100 of the value - I hoper this makes sence. ;D

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