Making a modulator around a 555 IC?

[rodair]

I trying to pulse a small 9 volt transistor Tone type of TX just like the old days of Ace Commander, Mattel TX and was thinking of using a 555 ic chip to so.....I build one but something is wrong....here is what I get to my actuator/rudder: at full right stick when the pulse train are very high (almost full tone) I get the actuator to respond accordingly giving my a full right rudder then at center stick position a normal pulse train 50% duty output pulse at the rudder swings left and right at ~2 Hz when my stick is center and but I couldn't any left rudder when the stick is to the left slower5 puse train the only thing I get is a slower full swing rudder like in center position still 50%?
What's wrong?
(note: the stick pot is 4 M ohms total that vary only 600 ohms with the total displacement of the stick left to right it can be adjust and lock to any value within the pot 4 M ohms range
If anyone can help here it would be more than welcome!.
rodair@3web.net:confused:

[cwatters]

I'm not sure I follow your explanation but it sounds like you are trying to run the 555 at about 2Hz? If my memory serves me correctly this will only work reliably if you are using the CMOS version of the 555 IC. I think they are all CMOS these days but perhaps not. The non CMOS devices had a high input leakage current (eg the uA you have flowing in the 4M resistor may not all be going into charging up the capacitor - some is leaking into the pin on the 555 - perhaps all of it!).

Are trying to make a 2Hz square wave with variable Mark/Space ratio? In which case it's possible that the 555 oscillator is stopping when the M/S ratio goes below/above a certain point. There might be some guidance in the applications section of the data sheets on this. I'm very rusty (The last time I used a 555 was 15 years ago) but I think the 555 works by generating a triangular waveform and then using a voltage comparator to convert it to a square wave. Perhaps the comparator only works correctly over a narrow analog voltage range. eg you can't get it to produce a M/S of 1:100 all the way up to 100:1 because this corresponds to a voltage range outside the range that the 555 comparator can handle. It's not a perfect chip.

[Mr.RC-CAM]

Sounds to me like your circuitry has been set up to vary frequency rather than duty cycle. Perhaps you should post a schematic so that others can see what you are doing.

The pulse frequency can be anything from 7 to about 25 PPS. I suggest something around 10 PPS. The duty cycle is what needs to be variable: 80/20% and 20/80% are at the extremes and 50/50% provides neutral.

For sure, use the CMOS version of the chip (LM555C) and do not allow any "unused" pins to float.

Regards,
Mr. RC-CAM

[rodair]

Rc-Cam,
I tried to "upload" a file it was to big....I send you an e-mail for the time being:D
I have to figure out a better way to upload...within limits:confused:
Roger

[rodair]

Thanks to Mr.RC-Cam, I able to post these diagrams,
the way that I did my set up is just like diag 'A" and I don't get what I'm aiming for: a modulator that will send a sq. signal "variable according to a stick pot BTW 4Kohms assy) to a small a Tone
Tx to be sent to an Rx and drive an swinging actuator l/h and r/h proportionally to the stick position (pot value P2 in diag "C" ) na the frq, in Hz should be set by P1. any one who can help me calculate the value of Ct ( charging electolitic capacitor?) P1 and to what value should I set P2 to start with with is more than welcome....I'm not good in electronic's and don't have all the apparatus requiremnt.
Thanks to all that reply and or give they're suggestions comments.
Roger

[rodair]

I guess that I was so happy that I was able to post my diagrams that I forgot to preview before posting. so here it is: I need help to calculate Ct ( chargng capacitor) when P2 is an adjustable pot able of setting of 0-4 Kohms for it's center position BUT is limited to a 600 ohms max. variance due to mecha. stick assy (max. left to right stick position.= 600 ohms) I also have to give a value to P1 that should set the frequency according to the book, the 2.2 uF tantalum between pin1 and 8 was given to me (to eleminate interference?) I would like the signal to at a freq of 2 hz? Suppose P1 at 100 ohms than is it possible to get the rudder being activated by the RX that is driven by the incomming signal to swing L/h to R/h the rudder of tne model every 1/2 sec.? Does this make sence? Please help!
Originally the TX RX where use in a remote toy car having only 2 functions: fwd. /rev. when a switch on the TX was depress the already activated motor in the rermote car changes direction...I'm trying to pulse the tx and run an actuator instead of the motor at the rx output Am I dreaming? for now I'm learning about the 555 ic and it's a pretty nice chip. May be you can't modulate analog (transistor type of cuircuitry with digital Ic chip (logic command codes)? I don't know. any help here is welcome.
Roger:confused:

[Mr.RC-CAM]

The problem with the given circuits is that they are VERY interactive. Pulse frequency will vary too much as duty cycle is changed. This might be solved with a two 555's slaved together: One used in the astable mode to set the pulse frequency and another used in one-shot mode for duty cycle.

I will think about what you want to do with the LM555 and see if I can throw some ideas at you. Maybe someone will chime in and save the day (my fingers are crossed).

Some comments:

P2 is an adjustable pot able of setting of 0-4 Kohms for it's center position BUT is limited to a 600 ohms max. variance due to mech stick assyYikes, you are really making this a tough one. Providing the necessary duty cycle range with those set of requirements is not an easy task (at least not for a small minded mortal like me). Getting the 20/80 thru 80/20 duty on a 4K pot, using only 600 ohms of it, is just not as easy as it sounds. I'm not sure if a simple LM555 circuit will solve the problem.

...the 2.2 uF tantalum between pin1 and 8 was given to me (to eleminate interference?)Its purpose is for power supply decoupling. The value is not critical -- a .1uF ceramic is fine too. Some applications do not need it.

I would like the signal to be a freq of 2 hzThat sounds too slow to me. I would suggest 5Hz minimum, 10Hz nominally. Fastest possible rate will depend on the performance of the actuator. From my experience with pulse propo radio systems, the pulse frequency needs to be tailored to your actuator -- but faster is usually better than slower. I never ran anything under 7PPS (7 Hz).

May be you can't modulate analog (transistor type of cuircuitry with digital Ic chip (logic command codes)?If you can pulse the actuator manually (e.g., blip a Tx mounted switch to wiggle the Rx), then using a pulser circuit WILL work just fine. I did that sort of trickery all the time in the late 1960's and 1970's.


Regards,
Mr. RC-CAM
www.rc-cam.com

[Mr.RC-CAM]

Well, I breadboarded my dual LM555 idea (I used an LM556). It gives a rock steady pulse rate over the full duty cycle using a 5K pot. I can easily get the 80/20 thru 20/80 duty if I use the full pot range.

The bad news: It will only eek out a 18% change over your required +/-600 ohm pot range. That is not enough for a rudder only pulse propo R/C model.

If you are set on using the LM555, then I am not going to be of much use to you. Hopefully someone else has a 555 timer solution to offer.

In my archives I do have the schematic to the old Jansson/Ace Commander Rudder Only Pulser. It is a 9V circuit that is easy to build (just three transistors) and one that I used quite often in the good ol' days. Frankly, it was the Holy Grail in its day. If you want to build it then I could create a schematic for you.

Frankly, a simple modern solution would be to use a PIC12C508 microcontroller. I have used it in situations that would normally have been handled by a complex "LM555" circuit. If you are a PIC programming fellow, then you might wish to consider using it. Even though it does not have a native analog input, stable A/D can be emulated on it. Sorry, but you would be on your own since I have other S/W projects to develop at this time.

Regards,
Mr. RC-CAM
www.rc-cam.com

[rodair]

That is more food in my plate then I ever ask for...., if I understand, the pot that I'm using at this moment is for the bird right in this aplication, what about if I get a bigger one 50 k or so pot to replace this one in the mechanical assembly of the stick then may be the 5k instead of 600 ohms will be achivable? on max displacement of the stick what I have to get is 5K range=max mecha. displacement=xdegree 360 degree 50k 60 degree=x .... food for taughts I don't know if it exist it as to be a long 1/4" shaft...or like you said to build from scratch arong a schematic.
Yes, I would appreciate if you get that diagram of your's around the 60's TX with only 3 transistors an working on 9 volts form the archeive is you have a change or when you'll cross that file.
BTW I went an bookmark your site...I didn't know that the best electronic man was actually the one answering my thread, I'm touch.....
Again many thanks for everything, tonight, I'll be able to say I've learn something.
:p

[Mr.RC-CAM]

...what about if I get a bigger one 50 k or so pot to replace this one in the mechanical assembly of the stick then may be the 5k instead of 600 ohms will be achievable?This would be a way to solve the limited range. But why bother? The Jansson circuit is a piece of cake.

I scanned the Ace/Jansson circuit directly from a prized copy of the May/June 1966 Grid Leaks Magazine. This magazine was the best R/C "e-zone" type publication of its day.

The three transistors are obsolete, but Mouser Electronics has them in their NTE line. As with all NTE branded parts, prices are a bit expensive. To save costs, the 2N2926 can be sub'd with a PN2222A and the 2N3638 can be sub'd with a PN3906. Data sheets are available from the Mouser site.

The 2N2646 is/was a very popular Unijunction Transistor (UJT) that has been discontinued. They used to sell for pennies. Again, the NTE parts at Mouser will work. Here is a data sheet to the 2N2646 UJT: http://www.halfin.com/semipp/2N2646.pdf

The stick pot is listed as a 10K on the schematic. I used 5K with good success. Your 4K should be fine too, but you may need to put another 2K - 5K in series resistor with it to get the 50/50 duty at center stick.

many thanks for everything, tonight, I'll be able to say I've learn something. You are welcome -- it was my pleasure.

Regards,
Mr. RC-CAM

[Mr.RC-CAM]

More comments:

The two switches that are shown are NOT needed. They were used with special actuators that had throttle control. On some actuators they will provide full left/right rudder.

The 2N3638 output transistor will directly drive transmitter keying circuits that are enabled when V+ (9V) is applied. All other Tx designs can be interfaced if you use a optoisolator (nearly any generic type, such as the PS2501 or H11A17). A 330 ohm resistor would be required to limit LED current.

Here are the pinouts to the transistors and details to the crude rudder only "stick" knob.

[rodair]

RC-CAM, since you breadboard the LM556 with a 5 K pot and it was successfull, would it be possible to have the wiring diagram of this one? since my project as it is at this moment is almost complete.....I should give this one a try......the 556 is like 2 -555 in the same IC right? so you use one part as a stable config. (freq?) and the other one as astable config. (duty cycle) ....right?
Roger

[Mr.RC-CAM]

Here is the circuit I built: Click Here to Download Drawing (http://www.rc-cam.com/projects/rc_pulse_pro_keyer.pdf)

Build it as-is before making any changes. Use any old 5K ohm linerar taper pot to act as the rudder control during your initial experiments. Then go attack the stick pot issue after you get acquainted with the circuit's operation.

Getting this circuit it to work to your satisaction will require further modifications. Frankly, the limited duty cycle range will be one tough bugger to solve. I don't have any good suggestions, so you are on your own.

I have a feeling you will end up using the Jansson pulser circuit. Please note that its parts count is VERY similar to my LM556 solution, so one is not simpler than the other to build.

Let us know what you find. Good luck!

Regards,
Mr. RC-CAM
www.rc-cam.com

[rodair]

Many thanks again, now I should have enough info to give a try a second time...I keep you post it may take a couple of days..:)

[MAVA]

I have a the schematics to the rudder only Ace Transmitter, Are you interested in having them?

On the transmiter the timming is done with a Astable circuit.

Let me know if you are interested?

Martin

[rodair]

Mava,
sure I do, both if you can.:D
e-mail them to me if you can.
Roger

[MAVA]

No problem, They will be in a Adobe Acrobat format.

Martin

[Mr.RC-CAM]

I would like a copy too. I built the ACE pulse system -- the schematics would be fun to see again.


Regards,
Mr. RC-CAM

[rodair]

:( mava, I didn't get the schematic, someone told memthat somehow my setting doesn't show my e-mail so here it is in case off:
rodair@3web.net
roger

[MAVA]

Sorry guys,

Here goes. I took me sevral days to find it. I found it last night.


Martin

[rodair]

MAVA
Now, you're cooking with GAZ!
I'll have a look and may try it.

[rodair]

It's too bad that I don't have a digital camerea to show you some pictures of what I did tryout and when throughout with the 555 modulator and TX in actions.
I will probably need help again.....it's not an easy field!
THE BEST PART OF IT:
I'm less "ignorant" about this sinple 555 ic and 556 ic chips! I beleive that it's a very nice clock! it might help in a lot of places if properly used.
Thanks too all that try to help me into this!
Roger

[Mr.RC-CAM]

Perhaps it is time to try the Ace/Jansson Pulser.

Regards,
Mr. RC-CAM

[chlluk]

Dear mava
I would really appreciate a copy of the Ace pulser circuit .
Best regards
Clive

[chlluk]

Mr Rc-Cam
Can i just confirm from the Ace pulser circuit that thc capacitor C1 is marked up,as 4,6 or 8 MFD. The legend is a bit faint when printed out. Thanks from all of the vintage flyers for your help.
Clive

[chlluk]

Dear all
Iam just getting ready to build this unit and noticed that capacitor C1 appears to have its positive pin down to the negative rail , is this correct or just a typo.
Clive

[DNA]

chlluk,

I have circuits for the Ace/Phelps and Ace/Sim-plus pulsers that
both use unijunction transistors, and it looks like you're right.
The C1 cap should have the plus lead going to the E of the
transistor. In the schematic shown, it's backwards.

And, yes, the cap. values are 8, 6, or 4 uf.

[chlluk]

Dear Dna
Thanks for your contribution, i would love a copy of the other pulsers schematics if thats at all possible. Im on,

longstaff@clive66.freeserve.co.uk

Any format will do , I can deal with most of them.
We are also working on a 'moden' pulser on this side of the pond based on the 555 IC, if it works out i will post the results. For those interested i also noticed that if the charge resistor on the unijuction transister is a changed for a pot we have elevator control as well.

Regards
Clive

[DNA]

Clive,

I put the two circuits in a zip file and emailed to you.
Enjoy.

[Mr.RC-CAM]

I put the two circuits in a zip file and emailed to you.
I would enjoy having a copy too.

As DNA mentioned, the C1 cap is shown backwards on the schematic. It is correctly shown in the PCB drawing. Cap values are 8/6/4 uF, depending on required pulse rate.

Regards,
Mr. RC-CAM

[chlluk]

Dear all
While the pulser gets worked on i will take a look at making up an actuater to take advantage of the three possible functions availible (ala rand). I will try and use the inards of a modern servo as a basis. I have a few close up photos of the rand to work from.
Clive

[DNA]

Geez, I had a Rand sitting in the shop for over 20 years, and
just threw it out a few months ago. It was fairly large and heavy
and not suitable for micro flight, but was ingenious the way it worked.

Zip file coming your way Rc.cam.

[chlluk]

hi DNA
you missed out on that one, two rand actuaters came up on ebay this month and both went for a lot of money , they would have paid for your thanks giving dinner.
Clive