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R/C toy car transmitter circuit

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by cyberquest, Apr 11, 2005.

  1. cyberquest

    cyberquest New Member

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    :( Hi All: Can anybody help. Who knows about R/C electronics.I'm new to r/c electronic transmitters,I purchase a radio control toy car kit to build,and it came with the schemayic for the TX and the RX.The car has a range of 40 to 50ft. I would like to increase that range to the max 1000FT. that is the max set by the FCC-PART-15. THEY STATED to me 1300ft =1/4 mile. BUT I don't need to go that far. A i know its more than 50 and 300ft. there are cars that can go 1000ft because i seen them and wittness this. Like the one i purchase can go 40-50ft that not far at all and has the same internal electronics as the ones that can go alot further. Can anybody tell me and explain to me. What i have to change on the circuit and which parts. Or just add to the circuit. This schematic can beseen at this website httP://www.elenco.com/manuals/rcc-7k.pdf. The manual is (rcc7k). Icould not post it my self on this forum do to i have no scanner to scan it at this time. Sorry. Thats why i inclued the website. I hope someone can help me who knows R/C Electronics. I would like to know what kind of circuit this transmitter is set up as,are the two transistors set up as a darlington pair,is it a emitter-fellower circuit.What kind of circuit is it set up as. is it a series-parallel or a series circuit. The right side of this transmitter. What i also need to know is the of this TX is how they calculated for the frequency with those parts they used,and the output amplifier is there a low-pass filter on its output stage.I know only some basic electronics and OHMS-LAWS. IF anybody could help me to understand to calculate the oscillator to set the frequency in the circuit.I would Apprecite any help and your time posted. PS the company i purchase this kit from they can not help me on this subject. I KNOW this is alot to ask. thank you for your help and any info you post. JJ..
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hi Cyberquest,
    I think I replied on another web-forum.
    Your transmitter doesn't give the max allowed power probably because it gives the max allowed harmonics that cause interference on other frequencies. My son's RC car looked like yours but was bigger and was powered by a 7.2V big rechargeable battery. It went very fast and had a range of at least 400 feet. Its good range was probably because its receiver was very sensitive. It could pickup transmitters a few blocks away! Whenever my son stopped it, it would start running around by itself!

    If you boost the power of your transmitter, you might be controlling RC toys all over town, causing radio and TV interference and asking for a visit from the RF cops.
     
  3. mstechca

    mstechca New Member

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    Why do you care?
    Be careful!

    There are frequencies that other people use around you. If you are able to jam those frequencies, then expect some trouble. I got caught a few times by my mom for screwing her T.V. up when I wasn't intending on transmitting on that frequency, and the transmitter was powered with a 9V battery.

    Your best bet is to get frequency information first. If the frequency is way up there in gigahertz where almost nobody goes, then you probably will be OK at transmitting at 1000 feet. I would suggest getting yourself licensed.

    Even ham operators can't transmit on certain frequencies without a license.

    and for the frequency, use the equation: 1 /(2 * pi * sqr(L * C))

    sqr = square root of, L = inductor, C = capacitor, pi = your PIE button on your calculator.
     
  4. dave

    Dave New Member

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  5. cyberquest

    cyberquest New Member

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    R/C toy car transmitter

    Hi again I understand what you're saying . BUT. I Check with my local FCC AGENCY. THEY TOLD ME any RF transmitters that is 100mW power output and under is find in my frequency band and does not have to be licensed. Plus these cars work at FT-bands that are licensed through the company who apply through the FCC for that band for the public to use these cars on. And 1000ft is within and under the range the FCC STATES IN fcc part-15 by law. Thats in the states where I'm locate. maybe the laws are different in your country. Or are you from the states. 100mW HAS a range just under 1300FT, thats stated by fcc part-15reg by law.Now as for CB thats a whole other avenue. They transmitter on AM and i think FM WITH output powers in WATTS. ANYWHERE FROM 3TO400 WATTS OR MORE. THIS IS WHAT I been told through the FCC. That WHY YOU need a licensed for CBs. not for a R/C TOY CAR. THERES always going to be some interferance with some frequencies on these small bands but that does not mean i need a licensed for a R/C CAR. GO IN TO RADIO SHACK AND ASK IF YOU NEED A LICENSED FOR A R/C CAR AND THERE ANSWER I BET YOU THEY WILL SAY NO. AS for the last part of your answer can you give me an example! please explain. this is what i need for you to be more elaborent on. I thank you for your time and your help. JJ 8)
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I think that your toy car is too cheap to have more range. Maybe its transmitter isn't correctly tuned. Maybe its receiver isn't correctly tuned and doesn't have enough gain. Maybe the factory had to reduce the gain of the receiver so that it doesn't overload when close to the transmitter.
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Your answer is really pretty simple! - buy a 'proper' radio control system for a model car, instead of the 'toy' you currently have.

    You're not likely to find any suitable DIY designs, nor are you likely to be capable of building and aligning one (if you could, you wouldn't need to be asking here!). The reason for the lack of DIY is that it's so cheap to buy them, why pay many times the cost for an inferior DIY system?, when a commercial one is so cheaply available - plus the encoder/decoder chips aren't usually available to individuals.
     
  8. cyberquest

    cyberquest New Member

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    R/C toy car transmitter

     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Wait a minute, Cyberquest!

    The transmitter was fully assembled by the factory so its details are not shown. It uses a cheap encoder IC that operates on only 3V. Q1, the 27MHz oscillator and Q2, the RF power output stage operate from 9V to get max output. But C6 is in a capacitive voltage divider with C5, and they are required to attenuate the output of the oscillator so that the IC's output isn't damaged by overvoltage. Therefore Q2 doesn't have enough drive to give much output. Also, the schematic doesn't show a capacitor across L2 to tune it to 27MHz and therefore the output is reduced further.

    You could try reducing the value of R6 in the transmitter to get more output. However it might only reduce the life of the battery.

    There isn't much you can do to the receiver since it is built into an IC.
    I am sorry that you have a cheap toy with only a 40 foot range. :cry:
     

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  10. cyberquest

    cyberquest New Member

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    R/C toy car transmitter

    to audioguru: I understand that the encoder operates on 3V. because it has a operating range of 2.2 to 5V . It uses a zener diode to regulate the 3V from the 9V power supply. the oscillator is set for the carrier band-wd of 29.9mhz but has a range of 27.0-27.9. do to the fact that the first xtal in the transmitter and not in the car. is basically solved by the wide open receiver designed. it will accept a singal around 27.9mhz ( if the car is tuned for 27) its not a specific tuned for a specific frequency. there is no xtal in the car just a crude receiver that takes in random noise from the antenna and filters out all frequency and lets throught the 27-27.9 range do to this open reciver design. if what you sad is ture in you answer. then i think mybe not to change any of the original design just add a third stage another power amplifier transistor to increase to 100mW with out over loading the power supply. 9V can handle 100mV and another stage.Can this be done. if not. explain why!. or can you gave me a circuit that would work for R/C cars. 100mW is the maximum power output that can be usedand i need. can you help. :( JJ
     
  11. JimB

    JimB Super Moderator Most Helpful Member

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    cyberquest, I think you have just provided the answers to your problem, the quote you:

    "wide open receiver", "crude receiver"

    and to be perfectly honest, the transmitter is no better.

    You have bought a childs toy, the radio spectrum around 27 Mhz is full of low power devices such as yours, all squirting out poor quality RF signals, there is also the CB radio stuff. Your simple receiver is taking all this and just cant decode your transmitter because of it.

    OK, increase the transmitter power, add a power amplifier stage to the existing circuit.
    But, to be quite honest, the best way to improve that transmitter is to start again from scratch, it was designed to provide a signal at minimal cost, to control a cheap toy car.


    The advice you are getting here may not be what you were hoping for but it is the truth.


    JimB
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Re: R/C toy car transmitter

    I just finished looking at toy car receivers on Google to confirm my suspicion that your "crude" receiver is just a single-transistor super-regenerative one. The IC in the receiver only decodes the demodulated pulses. Since super-regen receivers are easily overloaded, I advise you not to increase transmitter power. Sorry. :cry:
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Re: R/C toy car transmitter

    I don't know where you're making your prices up?, but a two channel radio control transmitter, receiver, with two servos, only costs £50 in the UK - and I'm sure you could get it for less if you looked hard!. In the USA it should be well under $100.

    I wasn't suggesting you buy a new car, just some proper radio gear to fit in it, your existing gear is only a toy - which is why it doesn't have any decent range.
     
  14. Roboticinfo

    Roboticinfo New Member

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    That car is a kit sold from elenco
    it is about $26:00 dollars or in that range.
    If you were to replace the electronics with the expensive rc, you would be at a total of around 75 to more for a rc car.
    I think he want's a cheap way to do it and also
    it still would not get a range of a 1000.
    Most likely only 300.

    So there is no way that he could get that range.
     
  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Re: Reply

    But seeing as you couldn't see the car at 300 feet, does it really matter?.
     
  16. Roboticinfo

    Roboticinfo New Member

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    True, but with a wireless camera
    depending on the price, you could get one that would be capable of getting even a more greater distance then 300 feet, but would jack up the price of the little toy rc kit.
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    When I bought the fairly good RC car for my son, I got it at an after Christmas sale, and it had the same price as a much cheaper one by mistake!
    It was so good that it must have had a "real" radio receiver instead of a cheap one-transistor super-regen.

    I get lots of stuff for a good deal.
    Over here, cashiers in food stores scan the bar-code of items for their price. Frequently their computer has the wrong (higher) price programmed. When you catch them scan the wrong price, "if it scans wrong, you get it for free"! I always catch them. :lol:

    Instead of having staff search through the perishables and throw out the expired items, the food stores here let customers do it. When you find an expired "best before" date on an item, take it and a fresh one to the cashier and you get the fresh one for free! :lol:

    Then there are the "guaranteed lowest price matching" marketing strategies for computers and stuff, but that's another story. :lol:
     
  18. cyberquest

    cyberquest New Member

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    R/C toy car transmitter

    Hi again: I looked in to this transmitter a little further and compared this with other one stage R/C TXmitters and found out. the transistors used are small singal power low gain db transistors in these circuits from the start. THE CIRCUIT in the transmitter in my car looks like it was designed with a similar transistor. but when I looked at the datasheets of small singal transistors some of them have a power ouput of 150mW TO 450mW and current gain Hfe 10-1000. How can this be. (Can some one EXPLAIN THIS). Is this the way they just design the circuit in the car I GOT. THE car I found out only puts out 4.1mW OF POWER. Which i also found out, is just little over 50ft.Can my circuit put out a higher power. but they used the lowest gain in the transistor for min-power output in the transmitter circuit for this car. or is it the combination of the circuit used with this kind of transistor. EXPLAIN!
    To GTmann .Sorry if i got your name wrong. But you hit the nail on the head. It seems like you know something about R/C cars this is what i wanted to do. Use a less exspensive car and hop-up the output power.to get a farther range. but it looks like this circuit in my transmitter is set and designed for a lower power with the parts they used. i could increase the gain for a higher power output just a little bit. but this would or could over load the circuit. As stated by audioguru, nigel,. I have not try it . One more thing I forgot to mention is the cars i witness that when over 300ft-up to 1000ft max. They did use a modified r/contoller that was made to go 300ft, and they did use a high range camara on there vehicle.This is what i like to do my self, on my uncles land where I live to ride around the land with out looking at the vehicle. This is something I would like to experiment with. Who wants to go 50ft in circles its borring. Try it some times. How could I get a decent radio controller and modified the circuit to increase the range to the distance of 1000ft. which is what i want. 1300ft is the max alouded by the FCC PART-15reg -law here in the states at 100mWatts. can you help. do you know of a circuit i could use. can anybody help.
     
  19. Roboticinfo

    Roboticinfo New Member

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    I do build pricey RC car's from ground up but the highest range I could think of would be 700 or 800 which would be off a rc helicopter which has a high range but not your range.


    You could control your car from the internet which would give you unlimited range.

    Also it is not to pricey and you could use a webcam.

    I think that would be the best way.

    What do you think?
     
  20. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Re: R/C toy car transmitter

    You require ten times the tranmitter power to double the range!. But, as Audioguru has already mentioned, your receiver is a really cheap design, so you'll never get any short of decent range from it, even by increasing the transmitter power substanially.
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hi Cyberquest,
    I got my son's Tyco RC car for less than $30.00CAN and saw it listed in the Sears catalog for about $120.00CAN. I know a good deal when I see one. Its 7.2V Ni-Cad rechargeable battery cost about $30.00CAN. It went to the end of my street about 400ft. away and would probably go farther but my street stops at the end. It would go faster than real cars on the street, about as fast as me on my rollerblades! :lol:
    If I remember correctly, it didn't use servos but used pulse-width-modulation for infinitely variable control of its steering and speed motors like cheap RadioShack cars have.

    I have a $10.00CAN micro (very tiny) RC car. It steers like yours (?), full left or full right. It has a built-in rechargeable battery that lasts about 45 seconds before needing an automatic 1 minute charge. Executives play with them on boardroom tables. Guys use their guts to make indoor RC ultra-light model airplanes. Their range covers an entire gym, farther than yours.

    My FM transmitter goes about 1km or more line-of-sight when received on a real radio. It uses a two-transistor RF circuit similar to yours. I had it transmitting more than about 200mW on the same frequency as a real but low-power station (1000 or 10,000 times more power than mine, but distant), and the RF cops didn't arrest me. It has high power because its whip antenna is the proper length for its frequency. At only 27MHz, yours would need to be about 11 feet long, and also the receiver's antenna!

    If it was available, maybe you should have got a more efficient 49MHz RC car. I did. :lol:
     

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