I need to count pulses---need a bit of help

[dr pepper]

2 4026's would give you a /99 counter and display the count on 2 7 seg displays, the carry out on the msd would give you the /100 signal to trigger the fans.
A simple mains plug in timer with a mains relay conected to its o/p would give you a 8 hour or whatever you want reset signal.
If your 2 second pulse input isnt clean, such as from a contact you'll need a 555 to clean it up.

 

[qrper]

Whoa! That's a great idea!

I am not lazy, but do you have a schematic for your suggestion or a data sheet that shows how to do this?

I could see how the led display would come in quite handy. I'd have a better idea if how many time the misters came on instead of waiting until the blowers go online

 

[dougy83]

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From **broken link removed**

You may want to use seven resistors for each display instead of just one: the brightness will depend on the number of segments lit if just using a single resistor.

The pin 5 (CO) of the lower device will have a rising edge on the 100th input clock (and on power on). The CO is high for half the counts, so you may want to add an edge detector and/or some other logic.

 

[qrper]

Thanks so much, Dougy83, that was so kind of you to take the time.

I don't have 4026s in stock, but I do have an open account with mouser. I'll order the parts in friday or saturday so I can have them over the 4th of july shutdown at my day job.

One thing many people don't understand is in a greenhouse, keeping the interior cool is harder than keeping it warm. Even last winter with 20 below temps, on a sunny day, the inside temperature hovered around 90ish degrees. Of course, at night, the heater system kicked in.

Misting in the summer, when the water evaporates, it takes heat with it, but too much water in a hot green house breeds critters and mold. So, fans run to keep humidity in check. Too much air and the CO2 nose dives.

thanks again!

 

[dougy83]

Too much air and the CO2 nose dives.

Do you have to supply your plants with CO2?

 

[dr pepper]

Commercial clock radio's tend to use only one resistor for the common of the led, and the brightness does vary with the displayed time, not really a problem, I've done it before it doesnt show unless its a high brightness display.

 

[qrper]

Do you have to supply your plants with CO2?

Yes, but depends on Time of year and size of the greenhouse and what's growing

 

[qrper]

**broken link removed**
From **broken link removed**

You may want to use seven resistors for each display instead of just one: the brightness will depend on the number of segments lit if just using a single resistor.

The pin 5 (CO) of the lower device will have a rising edge on the 100th input clock (and on power on). The CO is high for half the counts, so you may want to add an edge detector and/or some other logic.

Would it be possible then to add the "and" gate at CO and one of the other outputs so I'll get my high output for all 100 counts?
and...

to reset the counter, a high pulse on the reset pins of both ICs, so, I'd need to raise them from ground with let's say a 10K resistor and place the high pulse on the reset pins.

 

[dougy83]

If you use an AND gate, you'll get a pulse as long as the time between the 100th and 101st pulse. You'll also have to use quite a few inputs, and you'll also have a high pulse when you turn the device on (and whenever you reset it).

A perhaps more usable method is to detect the rising edge of the CO, and use a timer to mask the output on reset (and power-up). The values for the resistors and capacitors can be calculated using t=1.1*RC, and you want 1.1R1C1 to be the length of output pulse, R2C2 > R1C1, and 1.1R3C3 should be some small value (e.g. 100ms).

 

[qrper]

Interesting. And thank you for taking the time to draw out a schematic.

I use a car radiator fan to cool some of the greenhouse when the sun is out. I'll pick off a point on that control board when it senses the sun is up, and reset the counter. More than likely use a one shot (555) then use your suggestion on the CO output.

 

[dougy83]

No problem. If you state the nature of the sun detector output, you may be able to incorporate it without the need for the 555 just by rewiring the CD4093 NAND IC.