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cycle timer with 555 timer and 4020's

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kabona

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hey everyone i am trying to build a cycle timer so i can turn a small aqaurium pump on and off on intervals between 1-15 minutes.

i did some looking around on the internet and came across this for a schematic... assuming some dude whipped it up quick......


timer_RESETII.jpg


problem is i assembled it and the current going to the relay doesnt stop, wiring for the flip flop is wrong, therefore not sending a signal to the relay. someone mind taking a quick look at this and give me an opinion

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Capture2.PNG


i took some pics of my board... a little messy.... resistor with the tape and green wire sticking out the top is the set value on the 4013 (i just jumped it using the diode with no wire) to the 4020 off timer

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DSC02768.JPG
DSC02769.JPG
 
Hi kabona,

it would drive me crazy putting a circuit together with a "schematic" like that.

Besides that I guess you used the wrong value resistors. As far as I can see from the photo you used three resistors of 1K and one of 100Ω.

The only 1K resistor in the schematic is the power-on reset at the far right side of the picture connected to an 68µF electrolytic cap. You won't find that value anymore, except for bipolar electrolytics used for crossover circuits.

First check if you have a valid clock signal out of the timer IC (pin3). Then check the binary counters. Connect low current LEDs to outputs Q4 (pin7) and Q8 (pin13). They should flash every 16th respecively every 256th clock cycle. Adapt LED current limiting resistor to the power source you use. (Using 4.7KΩ you'll be on the safe side with the LEDs blinking dimly at a supply voltage of less than 12V.)

In the meanwhile I will design a "true" schematic which is easier to read because it contains (printed) pin numbers, which are not visible on the original instruction.

A 12 position rotary switch for ON and OFF time selection is nonsense in my opinion. Why would you want to switch on and off a device at the count of 1?

Using two 10 position DIP-switches the lowest count would mean an ON/OFF time of 32 seconds at a timer frequency of 1Hz.

Boncuk
 
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Hi kabona,

the power up reset works well with a 47µF cap - no reason to worry.

I guess the schematic makes the usage of the diodes clearer than the building instruction.

When power is applied to the circuit it starts with an active phase (seen by the green LED connected).

I suggest to investigate for wiring errors around the diodes.

(Simulation works like a charm.)

Boncuk
 

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ok so becausei just assumed what the guy at the electric store gave me was a 130k res. turned out to just be 130ohms. so i replaced the 130ohm resistor with 120k. So the timer is working now, but the values of something have to be wrong. The timer is working but with wrong timing, like Q4 which should be at 16 seconds is only at about 1/4 of a second, Q5 which should be 32 seconds is about 1/2 a second and so on.

i swapped out the 120k ohm resistor at the Vcc of the 555 Chip with a 480k, most time i can get with that is about 7 minutes on Q14. I need get to around 15 minutes. Should i just keep increasing the resistance?




BTW im not an electrician, i know some basics though and catch on quick... this timer chip thing is definately new to me and having fun... pretty fun working with chips like this!!! thanks again for the help people...
 
Hi kabona,

Timing with a large value electrolytic cap is problematic due to tolerances of those caps. Tolerance is normally 40% of the nominal value. So a 10µF cap might have a capacitance between 6 and 14µF - spoiling timing to a great deal.

Using a nonpolarized polypropene cap, e.g. WIMA MKS-2-5 1.0µF (tolerance 5%) the capacitance might be between 0.95 and 1.05µF.

This cap requires different resistor values. Using 330KΩ for Ra (connected between +UB and pin7 of the timer IC and 560KΩ for RB (connected between pin7 and pins2 and 6) the clock frequency is 0.995Hz at 61.4% duty cycle the longest delay time will be 4.528hours provided the cap has an accurate 1µF capacitance.

I also saw on your photo that you are using carbon film resistors which have a high positive temperature coefficient. Replace those with metal film resistors (to be determined by a 5 band colour code) which have a low temperature drift.

I also designed a single sided PCB layout for you. It requires seven wire jumps and measures 4.7X2.49inches.

BTW, an ON-time of 4.5 hours for an aquarium seems a bit low for me. I used to have the pump (+filter + heater) run 16 out of 24 hours.

Setting the clock frequency to 0.25Hz the longest programmable time period will increase to 18.2 hours

Regards

Boncuk
 
Thanks for your effort Boncuk, I like the circuit especially your addition of the DIP switches to make the cycle time better configurable. If you get a chance, I would be interested in the PCB layout but it has been a long time since this thread and I understand it you dont want to spend time looking for it.
 
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