Water level sensor auto to up - Page 1
Forum section: electronics / beginners

author: Idzanagi
author_rank: Contributor
timestamp: February 03, 2020, 08:03:31 pm
content: Hello guys,I was thinking to make a simple auto top-up for my fish tank. For this I ha bought from eBaya water pump:DC Voltage:3-5VFlow rate:1.2-1.6L/minOperating current (MA):100-200 MAAnd a contactless water level sensor:Signal Type: Voltage SignalWorking temperature: 0~60°CWorking voltage: DC5~24VOutput current: 300mAResponse time: 30 secondsOutput voltage: 0.5VCurrent consumption: 5mAand I had a few of these N MOSFETs:NTD3055L104 Datasheet:http://www.farnell.com/datasheets/2354279.pdf?_ga=2.87091932.51684700.1580662405-1659520191.1575453177&_gac=1.156421577.1580662405.CjwKCAiAg9rxBRADEiwAxKDTunwK6LIGNb0FcUEN7gutzKVJgo_CeV4LYp6WnKOd_959IvXdxC3W5xoCIUIQAvD_BwEI have never used Mosfets before so I am not sure that I did everything correctly or not. but there is the wiring:https://drive.google.com/open?id=1lZLvW55_A1Ed4BMtQ_eLx-Vu_jm8-hwQMy PSU is a simple USB charger: 5V 1AMy problem is that the pump does not get the 5V 200mA and this way is too weak to do the job.The sensor is turning it on and off so the MOSFET gets the signal. I measure the signal is 4.3V and maybe 1mA.When I directly connect the Pump to the power source it`s working fine. So I think I do something wrong with the MOSFET. As far as I understand the datasheet 4.3V should be enough.Does anyone have an idea what is the next step, what did I do wrong?Thanks!

author: floobydust
author_rank: Super Contributor
timestamp: February 03, 2020, 10:21:39 pm
content: Need more details about the water sensor, there are many different options they have. The non-contacting sensor modules can be analog or digital output, and source or sink current. It sounds like you are getting enough voltage to turn on the mosfet, yet the pump motor does not spin, which does not make sense.The really cheap (contacting) water sensors are one transistor affairs (emitter-follower) so their output voltage can be weak, not enought to fully turn on your mosfet.I would include a run timer so the pump cannot get stuck on and make a mess, i.e. if the sensor falls off the tank.

author: SmallCog
author_rank: Frequent Contributor
timestamp: February 04, 2020, 09:24:49 am
content: Have you given some thought to possible failure modes?Would suck if your tank overflowed...I’d suggest plumbing in an overflow back to your top up tank.

author: Idzanagi
author_rank: Contributor
timestamp: February 04, 2020, 10:32:02 am
content: Quote from: floobydust on February 03, 2020, 10:21:39 pmThank you Floody,The pump was working when the sensor gave the signal but the voltage on the pump was too weak to operate properly.As you said the MOSFET getting enough voltage but somehow when attached the signal to the gate Its dropped down 2.3V from 4.3. I don't know is there a shortage in the MOSFET or something else. I can measure 108Ohm between Gate and Drain so I think this means it cause the problem...I have decided to start over with an unused same MOSFET on a breadboard and this time I measured the right voltages.4.6V on the pump and around 4.3V on the signal. The pump now is strong and moving the water without a problem:https://drive.google.com/open?id=1lwIs7wXFC-BI30i0wLz5XciDBN4zdZVeThe sensor that I use is from eBay: cost about £7 and I found it kinda impressive. My fish tank glass is very thick but after calibration is working very accurately.There is a picture of it:https://drive.google.com/open?id=1m2uKMroP7RaGckJ6YlgyF8pjmmX2LgK3Also of the board itself:https://drive.google.com/open?id=1m50I1YJqjTG8d_gJjpPUc1GeD5OZ8QxCWhat kind of timer would you recommend?Quote from: SmallCog on February 04, 2020, 09:24:49 amThat is a good idea. Be honest I did not think about what if it fails. I will plumb an overflow back to the barrel.

author: Ian.M
author_rank: Super Contributor
timestamp: February 04, 2020, 11:30:34 am
content: The topup water will need filtering and oxygenating if you return the overflow to its container to prevent it becoming stagnant. At that point you are probably best off running the topup pump continuously or on a timer and letting the overflow height set the level it maintains, so your main filter/oxygenating setup can also handle the reserve container.Your original idea is only good if the topup water is kept near-sterile with negligible biological contaminants and nutrients, which would require the overflow to go to a drain or waste barrel rather than back into the reserve.

author: SmallCog
author_rank: Frequent Contributor
timestamp: February 04, 2020, 11:53:34 am
content: I was meaning an overflow that is only used when (or if) the sensor plays up.The other option is a sump filter. The water level in the tank is constant then.

author: Idzanagi
author_rank: Contributor
timestamp: February 04, 2020, 12:32:46 pm
content: This top up is just for replacing the evaporate water from the tank.I have a 20L barrel and just have to move around 2L of water daily. If the sensor plays up than I can put an overflow back to the Barrel until I get home to fix it. Thank you guys

author: floobydust
author_rank: Super Contributor
timestamp: February 04, 2020, 07:04:34 pm
content: I think the WS-03 non-contact pipe liquid level sensor has an open-collector output, so you need a pullup resistor.Also need a protection diode across the motor (+) and (-) to protect the MOSFET from the motor's back EMF. something like this schematic maybe

author: Idzanagi
author_rank: Contributor
timestamp: February 05, 2020, 10:47:22 am
content: Quote from: floobydust on February 04, 2020, 07:04:34 pmI soldered together last night and working fine. Added the diode and the resistor Thanks, learned a good practice.I am wondering is there any pull-up resistor built in the Ws-03.I am making a case for it and ready for a test day.What kind of timer did you mention?Does anyone have experience in this:Or any easy way to make an extended water pump cable waterproof?