electronic timer for CL

We had a talk at our club recently by a couple of electric freeflight chaps from a nearby club the thrust was a clever little timer mostly uesd for indoor freeflight models. extremely light weight. it is a simple electronic switch that is held in a the closed position by the voltage stored in a capacitor that is allowed to leak away in a controlled fashion. I don't understand the electronics but it seemed that there was an opportunity to use this in the smaller electric stunt models. Here is the circuit:-


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Mike,
Most of us now are using the JMP-2 or ZTRON-3 timers which offer the capability to control a Electronic Speed Control (ESC), a necessity for the newer brushless motors (since something has to take the place of the commutation function that brushes use to provide).

This one would work on small brushed motors where you wouldn't need a speed control. The main issue is that you don't have a throttle, which can be useful if you want a little adjustment (downward of course!).

There are fancier timers (and more costly) than the two I mentioned, but I have no first hand experience with them. Plus Igor Burger has shown how to program a simple chip to provide a similar function.

But you are right that this setup would be a simple inexpensive setup with small (than 1/2A??) planes. It depends on how resistive the "switch" chip is in the schematic. The other potential issue is that as the capcitor discharges through the 1MOhm resistor (a RC circuit with time scale =resistance*capacitance), there might be a relatively long period where the switch is slightly conducting, leading to a long drawn out landing---probably on a windy gusty day too!.

That and the relatively small changes in C and R will vary the time constant. temp, applied voltage, and humiidty, (7.5M) will affect it even if the FET switch is stable.

Simple but the added complexity of something with a PIC countdown timer seems well justified unless you want to run very brief bursts like the FF application.

Just my .02

Curt

> I don't understand the electronics but it seemed
>that there was an opportunity to use this in the smaller
>electric stunt models. Here is the circuit:-
>

It's the modern equivalent of an air-leak timer! An "electron-leak" timer.

Brett

...and if you listen VERY carefully...

Curt

I dunno.. I need to set MY timer to the nearest millisecond.. [photo not recovered: shocked.gif] Besides, if it ain't got a computer, what value is it? (nerk, nerk!)

That timer circuit is simplicity itself, there's a certain beauty to that.

Of course, you can also use something in between, e.g. a versatile little 555 timer and get better results with smaller and more practical component values. The 555 switch points are at fixed fractions of voltage supply. This makes it useful over a wide range of power supply voltages.

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A full 555 datasheet is available in PDF form at http://www.datasheetcatalog.com/datasheets_pdf/N/E/5/5/NE555.shtml

Google a bit more and you can find a ton of good application notes, and best of all, you can get this ubiquitous little part at your local Radio Shack or similar, at very low cost.

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"My milkshake brings all the boys to the yard,
And they're like: It's better than yours,
Dang right it's better than yours,
I can teach you,
But I have to charge." -Kelis

>I dunno.. I need to set MY timer to the nearest millisecond..
> [photo not recovered: shocked.gif] Besides, if it ain't got a computer, what value is it?
>(nerk, nerk!)

Oy Vey!


>
>Of course, you can also use something in between, e.g. a
>versatile little 555 timer and get better results with smaller
>and more practical component values. The 555 switch points are
>at fixed fractions of voltage supply. This makes it useful
>over a wide range of power supply voltages.
>

Yeah, just hook the motor/battery from pin 5 to pin 1, right? Good thing they're cheap....

But seriously, you still need the control FET - the timer just replaces the RC circuit, and for anything but a tiny motor the specified FET is not going to nearly cut it.

Brett

So true, unless your motor uses 2 ma or less!

Of course. A pass transistor or FET is still needed. I suggested the 555 because it is very stable and can operate over a large voltage and temperature range. It's amazing all the applications it has. A dual
timer version, the 565 part is even neater.

The other good news is that modern power MOSFET devices have performance approaching an ideal switch.

And your description of the simple R/C/FET circuit as an "air-leak timer" was particularly apropos.

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"Where there is an unknowable there is a promise." -Thornton Wilder

Sorry to digress, but this is for a CL airplane application. What's the voltage drop through these magic MOSFETs? I want to switch 1.3V at 500 mA.

Thanks,

Howard Rush
Bellevue, WA

Howard, I haven't used them myself for years, but the last time I did, I recall off resistance was in the tens megohms and the on resistance was a few (say a couple of) ohms. Power handling in amps with switch times in microseconds. As I said, essentially an ideal switch, and I'm sure they are improved by now. There's some reason they are used in the commercial motor controllers.

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"I'm not dumb, I just have a command of thoroughly useless information." -- Calvin

>Sorry to digress, but this is for a CL airplane application.
>What's the voltage drop through these magic MOSFETs? I want
>to switch 1.3V at 500 mA.
>
>Thanks,
>
>Howard Rush
>Bellevue, WA

Voltage drop in a MOSFET is just I*R. There is no saturation voltage drop as is the case for junction type transistors.
Good parts have Rds (on resistance) of a few mOhms.
So pick a device with a low enough on resistance and at .5 amp you could drop less than 10 mV.

The catch is that you need more than 1.3 volts to fully switch on a MOSFET. More like 2.5 volts for logic level drive parts.

This is also a limitation for the circuit in the first post for higher power applications.
As the gate voltage drops the FET will spend a long time in "linear" mode and could get quite hot.

If you have an application in mind and need some help picking a part, drop me an email.

Pat MacKenzie

Brett, pin 1 is Ground but pin 5 is Control Voltage.. Pin 7 (Discharge) is what you were thinking of, I'm sure. (Plusmore than those two pins are involved, of course.)

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"Ninety-nine per cent of the people in the world are fools and the rest of us are in great danger of contagion." -Thornton Wilder

>Brett, pin 1 is Ground but pin 5 is Control Voltage.. Pin 7
>(Discharge) is what you were thinking of, I'm sure. (Plusmore
>than those two pins are involved, of course.)

I'll go check my previous data. I may have hooked up (and blown up) more than a few 555 timer chips over the years, but the last time was years ago. As I said, they're cheap...

I like the RC circuit precisely *because* it doesn't look like a computer!

Brett

>>Brett, pin 1 is Ground but pin 5 is Control Voltage.. Pin
>7
>>(Discharge) is what you were thinking of, I'm sure.
>(Plusmore
>>than those two pins are involved, of course.)
>
> I'll go check my previous data.

Oops, I think we are both wrong, we want pins 1 and 3 and have those hooked across the switching FET. But you may need a buffer between the chip and the final switch - there's a healthy amount of current required for FETs large enough to throw the 15 amps or so with any margin. The BUZ71a is rated for 13 amps but you wouldn't want to run it at that for any length of time and you wouldn't expect it to last for long.

Brett

True, pin 3 is the drive for the internal transistor; it is the output of a flip/flop.. The BUZ71a you mentioned has an on resistance of .13 ohm, and it looks like a worst case leakage with 50V applied, and running hot at 125 C, of 100 uA.

It's a great part, but did you notice that it is NOT FOR NEW DESIGN? There's something newer and even better!

Dang, if only the world would move forward like electronic devices! ;->

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"A team effort is a lot of people doing what I say." -Michael Winner

Hey guys, just buy it for $30 and lower the bandwidth.
http://www.bsdmicrorc.com/products.cfm?catID=10006
Maybe you haven't heard, but there are guys out there actually flying ECL

Geez........

ok, I guess your just having fun.

>Hey guys, just buy it for $30 and lower the bandwidth.
>http://www.bsdmicrorc.com/products.cfm?catID=10006
>Maybe you haven't heard, but there are guys out there actually
>flying ECL
>

Really? I don't think that can work, can it?


Brett

Oh oh! We're busted. Engineers coning about electronic minutiae.. I'm sure some wonder why, but we actually enjoy tossing such things around.

(Don't get me started on my ideas for a tiny integrated controller/data acquisition/logger module for CL Stunt.. ;-> )

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"2 is not equal to 3 - not even for very large values of 2." -Grabel's Law

>(Don't get me started on my ideas for a tiny integrated
>controller/data acquisition/logger module for CL Stunt..
>;-> )
>


That was just so last year.



Kim.

>Hey guys, just buy it for $30 and lower the bandwidth.
>http://www.bsdmicrorc.com/products.cfm?catID=10006
>Maybe you haven't heard, but there are guys out there actually
>flying ECL
>
>Geez........
>
>ok, I guess your just having fun.

To show just how we enjinears think(?), I was puzzling about ECL, of course relating to Emitter Coupled Logic, (of course!) a very high speed, low impedance, current controlled type of digital logic circuitry, which uses a lot of power. You know, the sort of thing used in the old Cray computers? And trying my darndest to figure how that might possibly be useful in the application of Electric Control Line..

Well, DARRR, Larrrrr! (nerk, nerk!)

No wonder we can't get any women.

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"Don't wait for the last judgment. It takes place every day." -Albert Camus

>No wonder we can't get any women.
>

That and the fact we're older than the venerable 555!

Me, I'm yucking around with I2C and LVDS applications and Software Defined Radio--it drives the women crazy!

Curt

>
>>No wonder we can't get any women.
>>
>
>That and the fact we're older than the venerable 555!
>
>Me, I'm yucking around with I2C and LVDS applications and
>Software Defined Radio--it drives the women crazy!

Feh! This is the technology of love. Master the thermionic valve and the world will fall at your feet....


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JJ GZ-34/5AR4 rectifier (l), Telefunken ECC83/12AX7 dual triode (r)


Brett

Attachment #1, (jpg file)

now that would be the correct way to build a timer for an electrified old time stunt model. i would even allow a "delay relay".
sort of an old tube mounted heater timer.
the 555 timer would be only right for a 70's model
seriously though,you could also gate an scr from the 555 for any amount of current you need
Dave jr.

>now that would be the correct way to build a timer for an
>electrified old time stunt model. i would even allow a
>"delay relay".
>sort of an old tube mounted heater timer.

Yeah, but lifting a few B Batteries might not work so good on that Flying Clown. Maybe we need to add a generator to power the whole thing.

Brett

On Elmendorf AFB in Anchorage, I worked with an older ex-Navy EE student who frequently said he liked tubes, because "you can play with a tube". He remained upset about the defined direction of solid state current flow (from + to -, except in a source), in contrast to what the Navy had taught (electron flow, a la tube emitter to plate). In Anchorage, we amused ourselves by attempting to "ice skate" on Lake Spenard, (intoxicated, of course), and Gerald was always entertaining.

About the time we reached h-parameters, he dropped out of NMSU. I remember it well, as Gerald was the only one in our group who wasn't vulnerable to the military draft (1966 - Vietnam).

(We couldn't get any women back then either.)

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In high school I had an Ocean Hopper, which used a 12AT6 (triode). The 12AX7 (dual triode) was in a some TV sets. Those old enough to remember a mechanical tuning knob on a TV may also recall unplugging tubes and taking them to the self-tester at the local convenience store, even occasionally fixing your own TV set! You could also learn about stored energy in a cathode ray tube if you weren't careful.

Interesting that a FET (Field Effect Transistor) controls current flow with an electric field, similar to a tube, and was initially touted as a "quiet" device, with limited current handling ability. With development, the modern Power FET is something close to an ideal switch, with large current switching capability. Conventional transistors are controlled by current injected into a junction, they are current devices.

(Dang, but I'm old.) I'm sure you all wanted to hear about this stuff, my apologies for posting it.

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"Do not compute the totality of your poultry population until all the manifestations of incubation have been entirely completed." -William Jennings Bryan

Be very careful how you plug this thing into 120 VAC. Ideally, the .05 uF and 270K resistor are connected between the ac "neutral" and chassis. You plug it in wrong--and the ac "hot" is coupled to chassis through these same components. Thus the chassis becomes "hot" with respect to the surrounding universe! Not enough current flow through 270K to kill you, but you could get a nasty surprise.

Floyd in OR

The irony is that the 270K resistor is apparently intended to be a "bleeder" resistor, to keep the chassis from charging up. (I could be wrong, I often am..)

The Ocean Hopper was a Knight kit, and I don't recall if they carefully instructed the proper wiring of the two line AC power plug or not. But with the two line plug, you are still in potential danger if your house is not wired correctly.

Although the schematic, from the network, is dated '92, the kit was around in the 1960s, when we weren't so enlightened about electrical safety.

HOW did we end up here, talking about Ocean Hoppers, when the thread was talking about a super simple timer? (Well.. perhaps if I wouldn't hijack threads? My apologies, again.)

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"Lord, what fools these mortals be!" -Shakespeare

>Be very careful how you plug this thing into 120 VAC.
>Ideally, the .05 uF and 270K resistor are connected between
>the ac "neutral" and chassis. You plug it in
>wrong--and the ac "hot" is coupled to chassis
>through these same components. Thus the chassis becomes
>"hot" with respect to the surrounding universe! Not
>enough current flow through 270K to kill you, but you could
>get a nasty surprise.

A lot of these old radios and similar projects had the same problem. I don't know when they invented the polarized plug, but I bet I know why.

Brett

Larry,

It was pretty handy to get intoxicated since there was a large "BAR" sitting there on the shore of lake Spenard. At least there was in 1965-67. I used to love sitting by the window and watching planes with floats attached get up on the step so the could actually fly off.

Jim Pollock