Help with Countdown Lights

[jfinch]

Hi all,

I was hoping someone here could help me out.

We race rc airplanes and use a 1 minute starting clock to begin the race. This is a large analog "clock" driven by a 1 rpm motor with a mechanical switch that is activated at the top of the cylce to stop the clock (and bypassed with a mom switch to start the cycle). We want to use this same clock to time a different class of race plane that will require a 5 minute countdown. What I am envisioning is 4 red lights that all light up when the clock is started then at the end of the first minute (clock cycle) one of the lights goes out. This continues until the final minute and no lights are on (or all four blink?) then the clock stops when it reaches the top. I figured I'd use a reed switch and magnet to sense the clock hand at the 12 o'clock postion and a bunch of relays.

If you were going to do this, how would you do it?

 

[4pyros]

I would go solid state, You would need alot of relays to make say a shift register, and over time the relays would give you nothing but trouble. Who would fix it after a few years. For solid state you would need a 4017 decade counter a transistor and a relay to control the power to the motor. Think about it.

 

[jfinch]

Thanks 4pyros. The clock is powered by a 12v car battery. I've never heard of a 4017, but just googled it. It lights up sequentially. How do I keep all 4 lights on then have them drop out one at a time. Would the reed switch run directly into the clock pin (after dropping the battery voltage down to 5 or 6 v)? Will a transistor power a 10 watt light (via the 12 v battery)? I hope my questions are even making sense...

 

[#12]

It's all possible, but it's after midnight in the USA and after 5 am in England. Answers might be a bit slow right now.

 

[Boncuk]

I would go solid state, You would need alot of relays to make say a shift register, and over time the relays would give you nothing but trouble. Who would fix it after a few years. For solid state you would need a 4017 decade counter a transistor and a relay to control the power to the motor. Think about it.

Hi 4pyros,

how do you tell a 4017 to activate four outputs simultaneously?

I suggest to use a BCD coded count up/down circuit to set the desired starting value with a thumb wheel.

Boncuk

 

[Reloadron]

If you were going to do this, how would you do it?

I would start with an approach as Boncuk suggested. I would consider using a BCD programmable up / down counter maybe like the 74ls192 configured as a count down timer. Something to consider anyway, that or a similar chip.

Ron

 

[4pyros]

I all most forgot about the lights but you can still use the 4017. Wire relays to the outputs of the 4017 to drive the lights only use the NC contacts so the lights are on when the output of the 4017 is low. Use the 6th out put as your reset and motor drive and yes use your reed switch as the clock. Basicaly use the driver relays to reverse all the logic of the outputs. That should work right? Andy

 

[Boncuk]

I would start with an approach as Boncuk suggested. I would consider using a BCD programmable up / down counter maybe like the 74ls192 configured as a count down timer. Something to consider anyway, that or a similar chip.

Ron

just to add: use a BCD to decimal decoder (HEF4028) at the SN74LS192 outputs to control individual LEDs (one at a time) or use a 7 segment display to indicate time remaining in numbers.

Boncuk

 

[Boncuk]

I all most forgot about the lights but you can still use the 4017. Wire relays to the outputs of the 4017 to drive the lights only use the NC contacts so the lights are on when the output of the 4017 is low. Use the 6th out put as your reset and motor drive and yes use your reed switch as the clock. Basicaly use the driver relays to reverse all the logic of the outputs. That should work right? Andy

Hi 4pyros,

I wouldn't use a reed switch either unless a debouncing circuit is used. A miscount of 1 out of 4 is a mismatch of already 25%! Better use a Hall-sensor (TLE4905) and a small magnet on the clock.

I also guess a direct readout of remaining time (using a seven segment display) will be the optimum, saving on the BCD to decimal decoder.

Boncuk

 

[audioguru]

One of my new electric RC airplanes weighs 0.88oz (26 grams) complete with power battery and flies only about 10mph (16kmph). I can run faster when there is no wind and frequenctly it hovers when there is a light breeze. It can climb so high that I can barely see it.
Hawks chase it around the sky but it can fly loops around a hawk.

 

[jfinch]

I found a program that could simulate a 4017 (yenka) and played around last night. When I connected the output of the 4017 directly to the coil of a relay I ended up burning up either the 4017 or relay (sorry I don't remember which one burned... I messed around a lot and burned up lots of components ). Would need to power the relay through a transistor or was I just doing it wrong?

Also, just spent a little time looking for an example circuit using the 74LS192 count down timer and couldn't find any that really explained what was happening in the circuit so I'm at a bit of a loss exactly how to use that device. Can anyone explain, in terms a chemical engineer could understand, how that device works?

I like where all this is going, but I have some learning to do. I do appologize for my lack of electrical knowledge.

audioguru, keep flying! If interested, there are pictures and video of our races here: https://sites.google.com/site/cuprapylons/home (as a matter of fact, the clock in question is prominately displayed on the header graphic).

 

[4pyros]

I wouldn't use a reed switch either unless a debouncing circuit is used. A miscount of 1 out of 4 is a mismatch of already 25%! Better use a Hall-sensor (TLE4905) and a small magnet on the clock.

I also guess a direct readout of remaining time (using a seven segment display) will be the optimum, saving on the BCD to decimal decoder.

Boncuk; agreed

Uncle $crooge; Nice plane, has it ever been attacked?

Andy

 

[audioguru]

Uncle $crooge; Nice plane, has it ever been attacked?

Yes.
Hawks chased my Piper Cub airplane through the skies a few times and one time took a bite out of it.
My P-51 Mustang 2nd world war airplane is about the same small size, weighs a little more because it has an additional servo for the ailerons and flies faster than a hawk.
My friends and I fly circles around each other in the park. We haven't collided yet.
The Li-Po battery cell that powers the airplanes for about 10 and 15 minutes weighs only 3.4 or 4.1 grams.

 

[jfinch]

I typed out a reply earlier today and it said a moderator needed to look at before posting... How long does that usually take?

 

[Mike - K8LH]

One of my new electric RC airplanes weighs 0.88oz (26 grams) complete with power battery and flies only about 10mph (16kmph). I can run faster when there is no wind and frequenctly it hovers when there is a light breeze. It can climb so high that I can barely see it.
Hawks chase it around the sky but it can fly loops around a hawk.

**broken link removed**
One of the guys at our local airport was showing me this $25 ultra-lightweight IR controlled gyro-stabilized helicopter. It was amazing. That little electric tail motor is something like 1/4 or 3/8 inch in diameter. (xheli.com)

 

[Reloadron]

I typed out a reply earlier today and it said a moderator needed to look at before posting... How long does that usually take?

For new members (posters) the first several post are held in que for moderation. You should be fine for posting now.

I think.

Ron

 

[jfinch]

For new members (posters) the first several post are held in que for moderation. You should be fine for posting now.

I think.

Ron

Ok, I just didn't think it would take this long to moderate. I'll retype what I remember. There might be two of these messages show up...

I downloaded a fun app that lets you design circuits and then see how they run (Yenka) and messed around with the 4017. The output of the 4017 doesn't seem to be robust enough to power either a lamp or the coil of a relay directly. Using a transistor as a switch burns up the transistor too. I could be wiring these up wrong. Also I can find datasheets for the 74ls192 but I don't really understand how they work. Can someone explain that chip in layman terms that a chemical engineer would understand .

audioguru, rc is a blast! There are pictures and video of our racing here: Central Utah Pylon Racing Association (and the clock in question can be seen in the header graphic).

Thanks everyone!

 

[Boncuk]

I never experienced hawk attacks on my model planes. Hawks tried to get out their flightpath quickly.

The biggest model I flew was a B17 with 4m (13.5ft) wingspan and four engines.

Boncuk

 

[audioguru]

My RC airplanes are quiet and are smaller than hawks so they think my airplanes are something to eat.

There is a video on the internet of a huge model B-52 bomber with 8 model jet turbine engines (they are deafening). Each engine costs $5000. A second video shows it crashing.

 

[jfinch]

Hmmm. Another post waiting for moderation. Maybe it's because I included a link to a website? I'll try again, but without the direct link

I downloaded Yenka software that allows one to build/design a circuit and see if it works. I can't get the 4017 to output enough power to operate either a lamp or a relay coil. I can get the output to switch on a transistor but I then burn up the transistor...

<---- this chemical engineer needs some electronics help. Also, could someone explain in layman's terms what the 74ls192 chip does? I can't find any good example circuits that use it and explain what's happening.

Thanks everyone!

On the RC front... love that video of the B-52 crashing. If you want to see pictures and video of the racing we do you'll have to google "central utah pylon racing" (this is the link that I think is keeping my posts from posting). You can also see the clock in question in the header graphic of our web page.