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A water level indicator detects and indicates the level of water in an overhead tank and relays the information back to a control panel to indicate whether the tank has a high or low water level. In this tutorial, I am going to use the ULN2003 IC to create a simple, inexpensive water level indicator. Using this circuit you can easily control the wastage of water and electricity. Watch this video, for detailed step by step instructions on how to build this circuit and to know how this circuit works. Towards the end of the video I will also discuss whether its really worth building this circuit. Components Required For this tutorial we need: 1 x ULN2003 IC 8 x Different Color LEDs 8 x 1K Resistors 1 x 220Ohm Resistor 1 x Buzzer A Long Ribbon Cable, and A Breadboard or a Custom Built PCB About The ULN2003 IC The notch on the top indicates the starting and stopping points of the numberings of the chip. Starting from left to right going counterclockwise this is the Pin number 1 of the IC. On the left hand side Pin 1 to 7 are the Base Inputs. On the right hand side Pin 10 to 16 are the Collector Outputs. Pin 9 is the Common Cathode node for flyback diodes (required for inductive loads). And, Pin 8 is the Common Emitter shared by all channels of the IC. This pin is typically tied to ground. The UNL2003 IC contains 7 High Voltage, High Current NPN Darlington Transistor Arrays each rated at 50V, 500mA in a 16-pin DIP package. You can connect the IC directly to a digital logic (like Arduino or Raspberry Pi, TTL or 5V CMOS device) without an external dropping resistor. The ULN2003 is known for its high current and high voltage capacity. The Darlington pairs can be "paralleled" for higher current Output. To know more about this IC, please check out my "Tutorial No. 51: All About ULN2003 IC", the link is in the description below. Circuit Diagram The circuit is very simple. I have connected 7 LEDs to the 7 OUT Pins of the IC via 1K Resistors. On my left, are the 7 digital inputs which are connected to a ribbon cable. The other end of the ribbon is submerged in the water tank with exposed terminals at various heights to detect the water levels. Along with the 7 wires, there is an eighth wire that stays at the bottom of the tank and is connected to the +ve terminal. As the tank starts filling up, the water level rises and a conductive path is created between the positive terminal and the base of Darlington Transistor inside the IC. Hence a logic HIGH is sent to the Input Pin of the IC which leads to the corresponding OUT Pin to go LOW lighting up the LEDs one by one starting from the bottom Red to the top Green. The bottom Red LED indicates lack of water and the top Green LED indicates that the tank is 100% full. You can also add a buzzer to the circuit to get an audio indication when the tank is full. If you want to be super funky, you can also add a relay module which can turn on and off the water pump. Breadboard Demo Before assembling the components on a PCB, lets do a quick test on a breadboard to make sure our logic works as expected. For this demo, I am going to fill up a coffee mug with normal tap water. As you can see, the LED indicators go up from bottom Red to the top Green as I keep filling the mug. The buzzer starts buzzing when the mug is 100% full. Hence, our setup is working as expected. The Board So, this is how my board looks like in 2D and 3D. If you want to learn how to design a PCB, please check out my "Tutorial No. 45: Transformers PCB BADGE", the link is in the description below. Component Assembly Now, lets solder the components to the board. Lets first solder all the resistances to the board. Then, lets solder all the LEDs to the board. I am using a 3mm Green LED as the power indicator. Next, I am soldering the IC base to the board. Since I care a lot about my ICs and micro-controllers, I never solder them directly to the board. In case of an ICs, I always try to use an IC bases or if a base is not available I use female pin headers. After soldering the IC base, I am soldering the Buzzer to the board. Now to conclude the setup, I am soldering the Ribbon Cable to the board. For my setup, I am only using half a meter long cable. But in a real-world scenario, you will definitely need a cable longer than this. Final Demo So, this is how the final setup looks like. As the water level rises, a conductive path is created between the positive terminal and the base of Darlington Transistors inside the IC. This triggers a logic HIGH at the Input Pins of the IC and the corresponding OUT Pins goes LOW lighting up the LEDs one by one starting from the bottom Red to the top Green. When the mug is 100% full the top green LED lights up and we also hear a noises of the buzzer. Usability To be very frank, I see more disadvantages than advantages of using this IC in building a liquid level indicator. You may have a different opinion, but my opinion is based on the below facts: The choice of the probes that will remain submerged in the liquid has to be done very carefully as they: Rust, foul and deteriorate due to "corrosion" and "electrolysis" causing the LEDs to slowly fade and finally turn off. Hence the probes need to be cleaned and replaced every 2 - 3 years. This circuit will work well with tap water, however do not use this with salt water or with any flammable liquid. If in your house you get hard-water, there will be salt deposits on the probes and you will have to clean the salt deposits on a regular basis. This circuit will not work if you have a metal tank. Replacing the contact points with something "non-corrosive" may help but I will not put my bet on that. Another option is to have "large electrodes" which will have a low impedance even when covered with impurities. To conclude I would like to say that the ULN2003 is not the best device to use for this application. You might be better using a "CMOS buffer" or inverter which needs less water conductivity to operate and also gives a more sudden output change as the input voltage rises and falls, along with "non-corrosive large electrodes". Thanks Thanks again for checking my post. I hope it helps you. If you want to support me subscribe to my YouTube Channel: https://www.youtube.com/user/tarantula3 Video: View Full Blog Post: View References GitHub: View Gerber: View DataSheet: Download All About ULN2003 IC: View Transformers PCB BADGE: View DIY Relay Module: View Support My Work BTC: 1Hrr83W2zu2hmDcmYqZMhgPQ71oLj5b7v5 LTC: LPh69qxUqaHKYuFPJVJsNQjpBHWK7hZ9TZ DOGE: DEU2Wz3TK95119HMNZv2kpU7PkWbGNs9K3 ETH: 0xD64fb51C74E0206cB6702aB922C765c68B97dCD4 BAT: 0x9D9E77cA360b53cD89cc01dC37A5314C0113FFc3 LBC: bZ8ANEJFsd2MNFfpoxBhtFNPboh7PmD7M2 COS: bnb136ns6lfw4zs5hg4n85vdthaad7hq5m4gtkgf23 Memo: 572187879 BNB: 0xD64fb51C74E0206cB6702aB922C765c68B97dCD4 MATIC: 0xD64fb51C74E0206cB6702aB922C765c68B97dCD4 Thanks, ca gain in my next tutorial.

The UNL2003 IC contains 7 High Voltage, High Current NPN Darlington Transistor Arrays each rated at 50V, 500mA in a 16-pin DIP package. You can connect the IC directly to a digital logic (like Arduino or Raspberry Pi, TTL or 5V CMOS device) without an external dropping resistor. This IC features "common-cathode flyback diodes" for switching inductive loads. The ULN2003 is known for its high current and high voltage capacity. The Darlington pairs can be "paralleled" for higher current Output. The inputs are capable with TTL and 5v CMOS logic. Now, let's deep-dive and check out the internals of the IC and how it can be used in our projects. Pin Configuration and Functions The notch on the top indicates the starting and stopping points of the numberings of the chip. Starting from left to right going counterclockwise this is the Pin number 1 of the IC. * On the left hand side Pin 1 to 7 are the Base Inputs. * On the right hand side Pin 10 to 16 are the Collector Outputs. * Pin 9 is the Common Cathode node for flyback diodes (required for inductive loads). * And, Pin 8 is the Common Emitter shared by all channels of the IC. This pin is typically tied to ground. Detailed Description Inside the IC is the arrays of the 7 NPN "Darlington Transistors". Darlington Transistors were first invented in 1953 by Sidney Darlington. A Darlington pair is a circuit consisting of two Bipolar Transistors with the Emitter of one transistor connected to the Base of the other transistor. In this setup, the current amplified by the first transistor is further amplified by the second transistor. The collectors of both transistors are connected together. This configuration has a much higher current gain than each transistor taken separately. A small base current can make the pair switch to a much higher current. It appears as if it is just a single transistor, with only one base, one collector, and one emitter. Creating a high current gain approximately to the product of the gains of the two transistors: β Darlington = (β 1 * β 2) + β 1 + β 2 Since, β1 and β2 are high enough, we can write the above statement as: β Darlington ≈ β 1 * β 2 This connection creates the effect of a single transistor with a very high-current gain. The 7 outputs are all "Open Collector". By Open Collector, we mean a collector that is not attached to anything. It's just open. In order for an open collector output device to work, the open collector has to receive sufficient power. In order for an NPN transistor to work, the collector and the base both need to receive sufficient power. The base turns the transistor on, and then a much greater current flows from collector to emitter, but only if the collector has sufficient positive voltage. So if you want to connect a load to the Output of the chip with an open-collector-output, you must attach the load to a positive voltage source that is sufficient enough to drive the load. Hence, the +ve side of the load connects to the +ve voltage rail and the -ve side connects to the OUTPUT pin of the IC. Hence, when the Base current goes HIGH, the current flows from the collector to emitter and the Output logic goes LOW turning ON the LED (load) connected to the OUT pin of the IC and vice-versa. The maximum Output Current of a single OUTPUT pin is 500mA and the total emitter-terminal current is 2.5A as per the datasheet. Now, let's have a closer look at a single Darlington pair (internal circuit diagram) of the ULN2003 IC. The GPIO input voltage is converted to base current through a series base 2.7kΩ resistor connected between the Input and Base of the Darlington NPN junction. This allows the IC to connect directly to a digital logic (like Arduino, Raspberry Pi, TTL or 5V CMOS device) without the need of external dropping resistors operating at supply voltages of 5V or 3.3V. The 7.2kΩ and the 3kΩ resistors connected between the Base and the Emitter of each respective NPN transistor acts as pulldown resistors preventing floating states and suppressing the amount of leakage that may occur from the input. To maximize the effectiveness, these units contain "Suppression Diodes" for inductive loads. The diode connected between the OUT pin and the COM pin (PIN 9) is used to suppress the "kick-back voltage" from an inductive load which is generated when the NPN drivers are turned off and the stored energy of the coils causes a reverse flow of current. A reverse biased suppressing diode is also placed between the Base-Emitter and the Collector-Emitter pair to avoid the Parasitic nature of the NPN transistors. Pin 8 is connected to the GND. Device Functional Modes Inductive Load In case of an inductive load, when the COM pin is tied to a coil, the IC is able to drive inductive loads and suppress the kick-back voltage through the internal free-wheeling diodes. Resistive Load When driving a resistive load, a pullup resistor is needed in order for the IC to sink current and maintain a logic HIGH level. In this case the COM pin can be left floating (not connected). This device can operate over a wide temperature range between –40°C to 105°C. Applications Now, lets hook this IC to a circuit. As we know, the ULN2003 IC can easily drive a high-current or high-voltage (or both) device, which a Microcontroller or a Logic Device cannot tolerate. Hence, they are widely used in driving inductive loads like motors, solenoids and relays. 1. In my first example, I am going to light up a few LEDs using this IC I have connected 7 LEDs to the 7 OUT Pins of the IC via 220Ohm resistors. On my left, are the 7 digital inputs directly interfaced to either a Microcontroller or a TTL Digital Logic. When a logic HIGH is sent to the input pin the corresponding OUT pin goes LOW lighting up the LED. 2. In my second example, I am driving a Unipolar Stepper Motor using this IC In this setup, I am using Pin 1~4 for INPUT and Pin 13~16 for OUTPUT. Each OUT pin is rated at 500mA. Pin 9 has the spike suppressor diode, and is connected to the +ve terminal. By sending combinations of 0's and 1's to the 4 input pins we can rotate our stepper motor. I have used this setup in my award winning Video Tutorial: "NodeMCU Based - 3D Printed Indoor Gauge Thermometer" the link is in the description below. 3. In my third example, I am going to light-up a few AC Lightbulbs using this IC For high voltage applications, we can use RELAYS to control motors, heaters, lamps or AC circuits which themselves can draw a lot more electrical voltage/current and therefore power. We can hook up a maximum of 7 Relays to this IC. In my setup, I have connected 4 Relays to the 4 OUT pins of the IC. An AC Lightbulb is connected to the NO-pin of the relay. When we send a Digital HIGH to the INPUT pin the corresponding OUT pin goes LOW and current flows through the coil pulling the armature, completing the circuit and hence lighting up the 220V Light Bulb. Same as the previous setup, Pin 9 with the suppressor diode is tied back to the +ve terminal. 4. In my 4th example, I am going to show you guys how to obtain more than 500mA at the OUTPUT As we know that each of the OUT Pins are rated at 500mA, then how can I drive a 1Amp device? All we have to do is, tie 3 of the OUTPUT pins on the OUT side, and tie 3 of the corresponding INPUT Pins on the INPUT side. Now the 3 INPUT pins act like a single INPUT Pin. So basically, we can parallel the inputs to get a higher amplified value of paralleled output. You may ask, why did I combine 3 INPUTS and OUTPUTS and not just 2? As per the datasheet each pin is rated at 500mA but the total output is 2.5A (*** Page 4 of datasheet ****). Hence, 2.5A / 7 Pins = 0.36 Approx. So, 0.36 * 3 = 1.07Amp Approx. which is what we want. Areas of Application The ULN2003A produced by Texas Instruments can be used for: 1. Driving motors and solenoids 2. Can be used as a Relay Driver for high voltage application (7 relays at the max) 3. To drive high current loads using Digital Circuits 4. To drive high current LED's 5. To create a water level indicator circuit 6. As a LED and Gas Discharge Display Drivers 7. Can also be used as a logic buffer in digital circuits and more... For more information about the packaging and the material used, please have a look at the datasheet. The link is in the description below. Always consult a manufacturer's datasheet before assuming industrial conventions, no matter how intuitive or obvious they may be. "In the face of ambiguity, refuse the temptation to guess." - Zen of Python Thanks Thanks again for checking my post. I hope it helps you. If you want to support me subscribe to my YouTube Channel: https://www.youtube.com/user/tarantula3 Video: Watch Full Blog Post: Visit References DataSheet: Download Darlington transistor: View Open Collector Output: View Transistor–Transistor Logic: View Parasitic Structure: View Related Videos NodeMCU Based - 3D Printed Indoor Gauge Thermometer: View Acronyms TTL: Transistor–Transistor Logic CMOS: Complementary Metal–Oxide–Semiconductor Support My Work BTC: 1Hrr83W2zu2hmDcmYqZMhgPQ71oLj5b7v5 LTC: LPh69qxUqaHKYuFPJVJsNQjpBHWK7hZ9TZ DOGE: DEU2Wz3TK95119HMNZv2kpU7PkWbGNs9K3 ETH: 0xD64fb51C74E0206cB6702aB922C765c68B97dCD4 BAT: 0x9D9E77cA360b53cD89cc01dC37A5314C0113FFc3 LBC: bZ8ANEJFsd2MNFfpoxBhtFNPboh7PmD7M2 COS: bnb136ns6lfw4zs5hg4n85vdthaad7hq5m4gtkgf23 Memo: 572187879 BNB: 0xD64fb51C74E0206cB6702aB922C765c68B97dCD4 MATIC: 0xD64fb51C74E0206cB6702aB922C765c68B97dCD4 Thanks, ca again in my next tutorial.