Bitchar-G / Bitcharger Secretes Revealed! - RC Groups
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Dec 19, 2002, 06:52 PM
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Mr.RC-CAM's Avatar

Bitchar-G / Bitcharger Secretes Revealed!

How would like to:

- Know a little more about the Tx and Rx circuitry?
- Increase your transmitter's RF Power 10X for only $1?
- Add a two-speed motor control for free?
- See how to make a simple actuator coil?
- See an experimental pulse proportional BitCharger Tx?
- Read how some people consume vast quantities of free time in the endless pursuit of the perfect hack?

It's all there. Every last juicy detail on how Mr. RC-CAM transformed the tiny electronics parts from his R/C car into a useful miniature e-flier radio system: Bitchar-G Hack Madness

Be amazed, perplexed, and entertained. As always, admission is free.

Last edited by Mr.RC-CAM; Dec 20, 2002 at 04:20 PM.
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Dec 19, 2002, 07:21 PM
Just an average RC'er
Jim McPherson's Avatar
Thanks a lot for that! That's a great source of info! I'll have to try that out.

Dec 19, 2002, 07:56 PM
Only nerd in the village
In a word: FABULOUS!

My own Bit plane should have its debut this weekend.

Dec 20, 2002, 02:17 AM
Las Vegas Realtor
Inari's Avatar
Thanks for the info. Very insightful. Too much work for me though! I was really close with my model design using all the stock parts (motor, geartrain, RX, TX) but the range was terrible. I may try the 9v trick when I get motivated to work on it again.

Dec 20, 2002, 03:42 AM
Registered User
billystiltner's Avatar
Hey I just finished putting in the 9 volt battery and lm7805.
I increased the ariel on the rx to 4.1 feet - this only give me about 12 feet. then cut it down to about 9 inches.
That definitely increased the range but not to 250 ft. It gets glitchy about 15 feet and then wrks fine fartrher out i would say 30 feet then get glitchy again. It's also glitchy straight in front of the model 5 feet away. It's a 57 mHZ radio. I just hooked the lm7805 like this - desoldered tx pin 9 / pulled through to top of board, soldered ground of vreg to ground of tx, soldered input of vreg to battery +, soldered output of vreg to pin 9 with jumper around board. For a heatsink I just used a bunch of solder between 2 componet blobs hooked to ground strip on back of board. I looked at the datasheet for the lm78xx and kind of got the idea I needed no additional components. I broke the antenna
wire while grinding. It lost about 3 millimeters of the antenna connector. Would that have anything to do with the glitching.
I also measured 6 volts on the output of the vreg just hooked up to battery. The battery was fresh so I figured this was ok. The vreg is one of the small ones from a hard drive. It doesent get hot. How could I get the 250 ft range? Did I do anything wrong?

Your site is great.

I just put the stock arial back on the rx and tested with an unmodified tx and the modified one. The modified one has about 1 more ft range than the unmodified one. I am only using 2 1.2 volt nicds in the rx. would that have anything to do with it?
Last edited by billystiltner; Dec 20, 2002 at 04:03 AM.
Dec 20, 2002, 10:27 AM
Registered User
rustycage's Avatar
Great stuff! Well organized and very informative site.

Thank you!
Dec 20, 2002, 10:29 AM
RPV builder & operator
Pierre Audette's Avatar
Billy, do you know if your Tx has a crippling cap?
Dec 20, 2002, 10:59 AM
Registered User
Mr.RC-CAM's Avatar

There is something wrong with your installation. The LM7805 will provide 5VDC out when 7V to 35V is applied to it. For sure, 6V out indicates it is not wired correctly and may damage the TX2 IC. The TX2 chip will be damage when the applied voltage is 6V or higher. Voltages above 5V are not to be used.

You need decoupling caps on the LM7805 too or it may oscillate. I suggest a .1uF ceramic on the output and a 1uf electro on the input. This sort of practice should be shown on the part's data sheet.

There is no need for a heatsink. Only 30mA is drawn through the Vreg when a Tx button is pressed. I used the TO-92 packaged 78L05 part and it does not get hot during use.

Only the TX2 chip is powered by the 5V -- everything else is operated by 9V. Going from 3V to 9V should give you a huge range boost. If not, something is goofy. Are you sure your chip is a TX2?

BTW, I am using the stock TX whip antenna. Longer aerials are best added after the mod is working well. Inductor changes may be required for optimum range on the longer whip.

Last edited by Mr.RC-CAM; Dec 20, 2002 at 11:01 AM.
Dec 20, 2002, 02:23 PM
Registered User
billystiltner's Avatar
Thanks the voltage regulator is a ta78m05f.
I think its pretty much the same as the lm7805
except its surface mount. I found out what may have ben the problem. The antenna wire was broken and the battery in my ohm meter is about dead. I also had the regulator mounted on the bottom of the board. I moved it to the top and connected the output straight to vdd, the input to where vdd was connected and ran a jumper to ground. I still get more than 5 volts on the output.
I tried a half dead 9volt and got 3.7 volts on the output.
But anyway the range was increased to 40 feet. Probably more
but there was a telephone pole at 40 feet and thats where it lost the signal at the telephone pole.
Dec 20, 2002, 02:26 PM
Registered User
billystiltner's Avatar
oh the tx is a tx-2 underneath that it has j2c3la
is this the revision c with turbo?
Dec 20, 2002, 02:35 PM
Registered User
Mr.RC-CAM's Avatar
I still get more than 5 volts on the output.
Sounds like the reg's Vin and Vout are reversed or the part is defective. In those situations it tends to act like a brain dead resistor. Shown below are the pinouts to the various LM78M05 packages.

But, 40 feet sounds better. However, with the 25" antenna and some coil tweaks on the Rx, and a fresh 9V Tx battery, I would expect MUCH better range. Look over your work again. Then head off to an open area (local park) to see how far the range improves. Let us know what you find.

Dec 20, 2002, 02:42 PM
Registered User
Mr.RC-CAM's Avatar
Oh the tx is a tx-2 underneath that it has j2c3la. Is this the revision C with turbo?
That appears to be a Rev A part. I understand that the Rev C will be labeled as "TX2C."

I have not seen one myself. It should start appearing as soon as the inventory of the current chips is used up. It is backwards compatible with the old part, so the change will be painless to Tomy and the clone makers.

Dec 20, 2002, 03:23 PM
Registered User
billystiltner's Avatar
cool about the painless.

As far as I can tell its hooked up right. You might be qable to
see it in this pic. I dont know if anyone that hasnt seen it before can tell what it is though.
I don't have the caps on yet. Still going through the pdf datasheet
at fairchild.

Last edited by billystiltner; Dec 20, 2002 at 03:34 PM.
Dec 20, 2002, 03:32 PM
Registered User
billystiltner's Avatar
Ok I have the cutoff pin in the middle hooked up to ground.
Should I connect ground to the common heatsink thingy instead?
Dec 20, 2002, 03:48 PM
Registered User
Mr.RC-CAM's Avatar
Should I connect ground to the common heatsink thingy instead?
You should use the ground shown in the data sheet. However, if your ohmmeter shows that the cut leg and heatsink are common ("shorted" together), then the choice is yours.

I don't have the caps on yet. Still going through the pdf datasheet at fairchild.
For reliable operation you need the caps. The LM78X series tends to oscillate without them.

The caps are mentioned in the fine print of the data sheets on several of the pages. The mfgs' usually specify a minimum of .1uF on the output and .33uF on the input (low ESR caps). Attached is the exact fine print from the Fairchild data sheet.

With >7V in, the Vreg's output will be 4.9V to 5.1V. If you measure anything else then it is defective or there is a wiring error. Although fixing up the Vreg is not going to improve your range, it will ensure reliable operation and will prevent TX2 harm. Once you get this straightened out you can work on the range problem.


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