coutdown 555 timer values?

Link doesn't work John?

Hi All, the outputs are going to be used to trigger 6 separate digital voice recorders (radio shack Model: 276-1323) I was thinking something like (Mouser part number 433-812H ) PCB relay used to close the switch on the voice recorder.

The voice recorders will have various recorded messages encouraging the children to keep pedeling.

Thoughts?

Thanks again guys!

--- :-)

The tricky part is shortening up that first 555 pulse in astable mode (which is longer than the rest because of the need to get the timing cap up to 2/3Vcc from 0V (instead of 1/3Vcc) on startup) and getting all the shift register outputs to go high on startup.

Using something like three HC74's would solve the "start high" problem by using the Qbars as outputs, using their SET inputs for POR, and using their RESET inputs to start the timing sequence. Getting rid of the extended first pulse problem could be done by using a couple of

Schematic on abse as "555 countdown timer (from seb), or:

news: snipped-for-privacy@4ax.com

Then, of course, there's always:

VCC>------+----+ | | V+ | [RT] | | | [10K] [R7] +----|-\\ | | | | >--+-->180s +----|----|+/ | | V+ | | | [R6] | [10K] | +----|-\\ | | | | >--+-->150s +----|----|+/ | | V+ | | | [R5] | [10K] | +----|-\\ | | | | >--+-->120s +----|----|+/ | | V+ | | | [R4] | [10K] | +----|-\\ | | | | >--+-->90s +----|----|+/ | | V+ | | | [R3] | [10K] | +----|-\\ | | | | >--+-->60s +----|----|+/ | | V+ | | | [R2] | [10K] | +----|-\\ | | | | >--+-->30s +----|----|+/ | | | +----D [R1] | G--+ | [CT] S | | | | | GND>------+----+----+ | _ | R/T>---------------------+

In this circuit we use six comparators with references derived ratiometrically from Vcc, which will make the circuit insensitive to longish-term variations in Vcc. The circuit works by applying a short positive pulse to the gate of the MOSFET, which discharges CT and forces all of the inverting (-) inputs to the comparators lower than the reference voltages on their non-inverting (+) inputs. This will cause all of the outputs to go high. Then, when CT charges it will rise through each of the reference voltages on the + inputs sequentially, turning each of the comparators ON sequentially, forcing, and holding, their outputs low, one at a time.

In order to determine the widths of the various outputs we can use

Vcc T = RC ln ----------- = kRC Vcc - Vth

to determine what the voltages will be on the - inputs of the comparators at the times we're interested in.

-- John Fields Professional Circuit Designer

One of the great things about electronics is that "contrivers of contrivances" aren't limited to one and only one solution. Usually, there are many different solutions, some less expensive, some more elegant or smaller, and you can have many acceptable answers to your problem. It's not like a jigsaw puzzle.

I'm not sure about this, but I would think you actually want the first output to go active after 30 seconds, remain active for enough time to go through the voice recording, then go off. You want the second output to go active after 60 seconds, remain active for a few seconds, then go off. The third output starts at 90 seconds, and so on.

Either that, or you'd want the first output to go on as soon as the bike starts, and remain on for a few seconds. It goes off, and then at

All of the above responses have been based on the wording of your original post. With the 6 X CMOS 555 circuit, all of the outputs (and the relays) will turn on at the same time. The first relay would turn off after 30 seconds, the second after 60 seconds, and so on. You will have six module voices chirping different things continuously, and every 30 seconds, one of them will go silent until they are all stilled. Is that what you want? Carefully examine the wording of your first post. That is exactly what you asked for, and that's what Mr. Popelish, Mr. Fields and the rest have been discussing.

Please take a minute, and carefully think about what you want the electronics to actually do for you. Then write something down which really describes that action. Include how long you need each relay to be on, please. From what you've said, you probably actually need something completely different from what we've talked about.

By the way, don't feel too discouraged about this. Inadequate project description has snagged more engineers and electronics people than practically any other problem. It's a real gumption trap, because actually, you've made something that works -- it just doesn't work the way you want. Fortunately, you caught it before you wasted time making something that would not do what you need.

Thanks Chris

Hi all,

OK, Here is EXACTLY what the circuit needs to do. (Thanks Chris for making sure we are all on the same page and we don't all waste a lot of time due to misunderstanding.

Kid gets on exercise bike. Instructions instruct him to start pedaling and then push the start button. (I thought this would be necessary so that the missing pulse detector doesn't immediately restart the routine because it thinks the kid has stopped pedaling)

After 30 seconds a prerecorded voice tells the kid he's doing good, keep going, yada, yada..

At the 60 second mark another a prerecorded voice tells the kid he's doing good, keep going, yada, yada..

At the 90 sec... and so forth

At the 3 minute mark the final prerecorded voice unit sings him praise (I'll probably add a relay here so flashing lights or whatever can also add to the grand finally) and then the whole thing shuts down and waits for the next victim, er, I mean rider.

If the child stops pedaling or pedals so slow the entire circuit should reset forcing the rider to start pedaling, hit the start button etc.

The digital voice recorders have two buttons on them (radio shack Model: 276-1323), one you press to record your message, the other to play it back. It's a momentary contact switch so I don't think the trigger out to the voice recorder needs to stay on for more then a few milliseconds or so.

I have a proximity sensor and amplifier of the type commonly used on automation equipment to sense if the wheel is turning. Alternately I could use a reed relay as suggested earlier.

I really can't think of anything else to add.

Thanks guys, someday this project will make a lot of kids happier and in better physical shape!

Lawrence

I think this is easily solvable by using a pair of capacitors in series across the supply as the timing capacitor. If you use one capacitor about twice as large as the outer, the mid point voltage will begin the first timing cycle at about 1/3rd of the total voltage, just like it will be at the end of the next cycle.

This is a lot simpler than a whole batch of 555s running in parallel.

That only helps if the supply variations happen on a much longer time scale than the timing cycle. If there is 120 Hz ripple during a 30 second time phase, the ripple will shorten the period.

--- Aaarghhhh!!!

This is what you said you needed: ___ T1____| |______________________________ _______ T2____| |__________________________ ___________ T3____| |______________________ _______________ T4____| |__________________ ___________________ T5____| |______________ _______________________ T6____| |__________

But, according to what you posted above, you need the following instead:

-->| || |

You need a C555 and a cmos 4017, along with some transistors or relays to act as momentary switches.

On the other hand, you could use a "winbond ISD4002", along with a bit of glue (or a microcontroller) to do the entire thing, replacing the radio shack digital recorders. (they probably contain this chip, a mic, a speaker, and a battery.)

Or, you could use an eprom and some glue logic to replace the pricy ISD4002 chip. This would probably be the cheapest option, although getting the audio right might be a chore.

I know the thread took a left turn, but I'll just point out that one may want to use a constant current source to charge CT. Then, all the resistors can be identical. If I is constant, dV/dt is also constant. One can get quad packages of comparators...

Elegant solution. "Mikey likes it!"

Ed

Yes, John, this is correct. I sent you an email with a small photo of the voice recorder circuit board.

It appears the playback button pulls a trace to ground when the button is pushed.

Thanks again,

Lawrence

--- OK.

I got your email, but it was empty.

I've posted a schematic of a circuit which should do what you want, and a fairly loose circuit description of it to abse and, since you don't have access to binaries through google, emailed it to you as well.

If you have any questions it would be nice if you posed them to the group so that we can all follow your progress.

-- John Fields Professional Circuit Designer