Hello everyone!
I have recently received the stater kit from Adafruit and started tinkering with the Arduino :
For my "HydroDuino" (automated hydroponics using the arduino) project
-i am currently trying to control a 5-12V water pump (basic on /off ) using one digital pin
-i need very precise timing in order to avoid overflow : this part works very well (tested with a simple led)
-i am not really good at electronics but after looking around i decided to go with a tip 120 transistor (with a diode for security) (schematics found here Fortellerorkesteret | Connect the Dots example
More info etc in my blog http://www.kaosat.net/?tag=hydroduino
THE PROBLEM:
- i am having HUGE speed fluctuations in the pump, so each and every time i start the system, i get different speeds, which pretty much defeats the whole “precise timing for a precise filling”.
*o in a lot of cases the motor starts of veeery slowly, and the speedup rate to an acceptable level always varies
o sometimes about halfway through the timing interval (set at 180 seconds for now), i will get a sudden decrease in power : my guess is this is tied to the tip120 transistor, and the lack of sufficient "differential" : i managed to reduce this problem somewhat by exchanging the 1k transistor that goes to the base from the Arduino digital pin with a lower rated resistor
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these problems are unlikely to come directly from the pump as i did not have such fluctuation when running it directly on the power supply
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i am also aware that using a cheap 8$ pump which eats up 2.2A at 5v (twice what was indicated on the seller's site) is also begging for problems
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I am not really good at electronics, but from what i gathered, i might need to add a few capacitors to smooth out the current and reduce the spikes?. like here ? http://www.tigoe.net/pcomp/code/category/Picbasic%20Pro/62
Sorry for my obvious lack of mastery in this field, but i am more than willing to learn
Any help , comment or suggestions is appreciated!
Thanks in advance