Countdown circuit with switching for pneumatic bazooka

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cobast

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Hi guys. I know bugger-all about designing circuits and could do with your help. I'm making a pneumatic bazooka to fire baseballs for my son to practice hitting. The commercial unit (Zooka) has a microprocessor for all sorts of controls. The thing I want to replicate is the count down to the firing of the ball. The sequence is, for the first 3 seconds an LED and a buzzer is momentarily activated each second or there abouts). At the fourth second a solenoid is activated to open the valve (irrigation type) and the bazooka fires. Essentially: beep,,,beep,,,beep,,,Bang. So it's really a count down circuit I guess. It would be powered by a 12V battery. The solenoids are usually 24v. Would the 12v car battery be sufficient to operate the solenoid? I've Googled for hours and been to electronics shops without much luck. So I need some help. Does anyone have some ideas? Thanks in advance.
 
Wouldn't giving a countdown be a poor type of training? I mean, a pitcher doesn't give you a countdown so why train someone to time themselves based on one?
 
Oznog said:
... a pitcher doesn't give you a countdown ...
Click to expand...
He does, however, give you the wind-up, which is a pretty good indication he's about to pitch ...

I would think this could be accomplished with a relatively simple sequencer using a 4017 and a 555, with a power transistor or SCR to fire the solenoid when the end of the timing cycle is reached.
JB
 
A Microcontroller would be cheap and easy, but you need a programmer, compiler, etc. etc. (if you were Nigel, just the programmer )

So jbeng has the best answer.

On the 12V to run the 24V seloniod, not sure, but you can not hurt them to try it a couple times.

If the this does file, get a buzzer to go in the circuit, is the LED required?
 
I wouldn't expect a 24v solenoid to work too well on a 12 volt supply. However, instead of a single 12v car battery to power things, two 12v motorcycle batteries in series would give 24v and plenty of current to operate the solenoid valve. Together, they would probably weigh less than the car battery, too.
JB
 
Ron H, in the commercial unit (Zooka) the ball being rolled down the barrel breaks an optical sensor system mounted at the barrel end. This isn't that important. It's more of a "nice to have" as I could put in a manual triggering switch for simplicity. The main thing I'm after is a circuit diagram for the countdown signal and firing. I could build mechanical switching (I'm an aircraft maintenance engineer) but I figure I should move into something more high tech / electronic. That's why I need the help of you guys.
 
I've got a circuit for you, unless your solenoid draws a lot of current. Do you know how much it requires (at 24V), and how long it has to be energized in order to pitch the ball?
 
Ron H, I believe the solenoids draw a max of 1 amp though most only draw 3/4 of an amp and are open for a second or so.
 
Here is the schematic and waveforms for the start switch (bottom trace), LED current (middle trace), and solenoid voltage (top trace).
You can use a different MOSFET for the solenoid driver, as long as Rds(on) is less than about 0.5 ohms. The other MOSFETs could be replaced with NPN transistors, each with a base current lmiting resistor. Alternately, the LED drivers could be NPN emitter followers, which would save you the base current limiting resistors. I just happen to like 2N7000 (or 2N7002). 8)
The rate of LED flash and the time until the pitch is adjustable with R5, and could be changed to basically any rate by changing C1.
 

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Wow, Ron. Your circuit is nearly identical to the one I have drawn up, with a few differences. My circuit uses bipolar transistors instead of mosfets. I also diode OR'd the Q1,3,5 lines and use only one transistor to drive an led and a beeper. I also have a transistor driving a "ready" led on the Q8/-CE line of the 4017. I let the 555 free-run and use a momentary switch to reset the 4017, starting the sequence. With those few execeptions, our circuits are virtually the same. What sim program are you using?
Jeff
 
Jeff, I drew and simulated it on LTSpice (SwitcherCAD III). Great minds think alike. :lol:
I reset the clock with the switch so the delay time would be exactly the same each time you release the start button. I forgot to put in the buzzer, but it can just be put across the LED/resistor.
 
Thanks Guys, I appreciate your efforts. If I take this circuit diagram down to Jaycar (our local electronics outlet) will they be able to read the diagram and just hand over a pile of components? I mean, in your diagram have you used icons that are recognised world wide?
Once again, thanks for your help. :wink:
 
Yeah, all the component values are printed there, the shop should have no trouble getting them.
 
Mr. EM, For my info, I take it those inverted triangular icons at the ends of the "wires" are just a different symbol for earth or a common (-) bus of the circuit?? :?:
 
Hiya Cobalt,
Yep those inverted triangles are for earth. Now you mention you're going to Jaycar so I assume you are in Oz. I find it pay to look at the prices of the components and compare them with Dick Smith, Alltronics then Jaycar. I just got the new jaycar cattledog and man have they ramped up the price on most stuff so I tend to give them a wide berth where I can. Depending where your located there might be some other shops that kill the big 3 electronic ripoff merchants for price so it will pay to look around. I know the component count won't cost too much but this advise is for the longer term mainly.

Cheers Bryan
 
Thanks Brian, Yeah, I'm in Cronulla / Sydney. I'll check out Dick Smiths then. We don't have Alltronics as far as I know. I've got my new Jaycar catalogue i front of me now trying to sus things out while I do googles for electronic stuff.
Thanks for the advice.
The Jaycar guy suggested I get a Flexitimer (page 28)to run some digital display kit (can't find it) and then get a signal amplifier kit (or something) that can tap off from the individual signals to the segments of the digital display. i.e Have the coutdown always starting at 3. Tap into the top R/H segment of the seven segment display to feed to the LED and buzzer. Tap into the top L/H segment to feed to the solenoid. Of course relays and extras but this was just of the top of his head and would cost around $30-$40. Sounds OK to me a nooby with mechanical background. But the circuit by Ron H seems more ????? seems better!
Reggies, Chris
 
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