Water level indicator for Eureka-3M. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Water level indicator for Eureka-3M. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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Owners of small-sized washing machines of the Evrika family are interested in reliable indication of the water level. One such electronic indicator was described in the article by V. Karevsky "Water level indicator for Evrika" (in the September issue of the Radio magazine for 1996). However, for machines of a later release - Evrika-3M - the recommendations contained in This article turned out to be unacceptable.For those who have purchased new machines, we suggest that you familiarize yourself with the indicator, which is described in the material published below.

In "Eureka-3M" for washing and rinsing, only one (and not two, as in "Eureka") water level is provided, corresponding to approximately one third of the height of the tank. Since the drum filled with laundry blocks almost the entire space of the tank visible from the outside, it is practically impossible to visually determine whether the required water level has been reached or not. In addition, instead of the water-measuring glass tube available in the old machine, "Eureka-3M" is equipped with a more convenient to use, but at the same time very unreliable in operation, float mechanism with a button that pops out. This primitive water level indicator not only constantly sticks, but over time literally falls apart into its component parts, which are not so easy to remove from under the bulky drum in the tank.

In order to save the owners of Eureka-3M from the troubles associated with the operation of this washing machine, I propose to replace the unreliable mechanical unit in it with a simple electronic device.

The indicator (see figure) is made on three transistors VT1-VT3 and one two-color LED HL1 (ALC331A). The washing tank of the machine is connected to a conditional case of the display device isolated from the mains, which acts as one of the contacts of sensor B1. The other contact of the sensor is a metal bar lowered into the tank to the required depth and electrically isolated from it.

Water level indicator for Evrika-3M

The washing machine is connected to the network using a standard plug, to which the winding I of the transformer T1 is also connected. The alternating voltage from its winding II is rectified by the diode bridge VD2 and smoothed out by the capacitor C1. On the transistor VT3, the zener diode VD1 and the resistors R6, R7, the simplest serial stabilizer is made. A stabilized DC voltage (about 8 V) is connected to the top wire and the case according to the scheme.

The indicator works as follows. When the tank of the machine is empty and the plug is connected to the network, sensor B1 is "in the air", and therefore the transistor VT1 (connected according to the emitter follower circuit) is closed. The current flowing through the HL1.1 LED (green) is very small (about 40 μA) and it is extinguished. Transistor VT2 is open and LED HL1.2 (red) is on.

As soon as the tank of the machine is filled with water so much that the sensor pin B1 is connected (through conductive water) to the body, the transistor VT1 will open and the HL1.1 LED will light up. The transistor VT2 will close, and the HL1.2 LED will turn off. Thus, the ignition of the green LED HL1.1 indicates that the desired water level in the tank has been reached and the need to stop filling it.

During the washing process, due to fluctuations in the water level, the HL1.1 and HL1.2 LEDs alternately glow either green or red. After the start of draining the used washing solution, the red LED HL1.2 lights up again, and the green HL1.1 goes out.

The HL1 LED can be easily replaced with two separate LEDs, for example, AL307NM (HL1.1) and AL307KM (HL1.2). Moreover, you can simplify the device by eliminating the red LED HL1.2, transistor VT2 and resistors R3 - R5. But the option shown in the figure is more preferable, since the same LED all the time indicates that the machine is connected to the network. And according to the instruction manual, "it is FORBIDDEN to touch the body of the machine and grounded parts (pipelines, taps, baths) at the same time." Since the Evrika-3M semi-automatic washing machine (SMP-3B models) does not have a special network indicator, a home-made water level indicator in the tank will simultaneously act as a signaling device that warns the user about the emerging danger during washing.

Transistors KT3102G (VT1 and VT3) can be replaced with KT3102E, and KT3107K with KT3107L. The KS175A (VD1) zener diode will completely replace the KS475A, KS168A or KS468A. Instead of a KD906A (VD2) diode bridge, you can use KD906B or KD906V, or assemble an ordinary bridge on four separate diodes, for example, KD102A, KD102B, KD103A or KD103B. All resistors are MLT-0,125, OMLT-0,125 or VS-0,125. Capacitor C1 - any oxide, with a rated voltage of at least 15 V. Transformer T1 is used ready - incandescent from an old tube TV. In idle mode, its secondary winding should have an alternating voltage of about 7,5 V.

All parts (except for the sensor, transformer and LED) are mounted on a plastic board measuring 60 x 60 mm. Installation - printed or hinged. The LED is glued with Moment glue to the upper plastic base. They do it this way: in the front nameplate and the panel itself above the inscription "Eureka-3M", a through hole is carefully drilled first with a drill with a diameter of 3 mm (roughly), and then with a diameter of 5 mm (cleanly). An LED is inserted into the resulting hole on the inside of the machine and glued.

Before proceeding with the installation of contact sensor B1, the old float indicator must be removed from the machine.

To do this, the white button of the old water level indicator is raised with tweezers to the level of the "red border" and fixed in this position by pressing the button against its guide. Then they grab the button with pliers and pull it out along with a red plastic tube put on the button - the actual color indicator. The rest of the parts - the metal restrictive washer, the wire rod-pusher and the plastic float itself - will fall to the bottom of the tank.

To remove them from there, and at the same time all foreign objects that accidentally got into the tank, the car is carefully turned on its side, after placing several old thick magazines under it so that you can grab its side wall. After that, they turn the car up with wheels and, having lifted it, install it on two stools with soft seats placed close to each other. At the same time, the handle of the operation switch must hang down without touching the stools! Then six (out of eight) screws M6 fastening the side walls of the machine are unscrewed, three of them are removed. The fourth wall (through which the network wire is passed) remains in place. Next, unscrew six M8 bolts with nuts securing the tank to two metal corners on the upper plastic base of the machine.

Then, grasping a massive cast-iron damper load, on the one hand, and a large belt drive pulley, on the other, the tank, together with the bottom of the machine, its frame, the working electric motor and other parts, is carefully lifted above the base, and into the resulting gap from both sides stack all the same magazines. Now it will be easy to clean the tank cavity of everything foreign.

Even before the tank is separated from the base, a projection of the axis of the float level indicator button, or rather its cylindrical guide, is applied with a soft pencil on its side wall. This line will allow you to drill a hole with a diameter of 3 mm at a distance of 4 ... 5 mm from the top edge (now it is at the bottom) of the tank. After that, a thin bridge in the stainless steel of the tank is removed with a round file, giving the cut the shape of the Latin letter "U". It is through this cutout that the wire from sensor B1 will pass.

Next, the tank is again fixed on the base and the machine is turned over to its normal position. In the former cylindrical guide of the button, a hot, sharp nail without a cap (about 2 mm in diameter and about 20 mm long) carefully burns a through hole (it is important not to damage the outer "shell" of the base!) So that the wire from the sensor pin B1 can be passed through it. The wire must pass from the top 21 mm hole (from the guide button) in the plastic base to the inside of the machine. The axis of this hole is located at a distance of approximately 5 mm from the upper edge of the cylindrical guide and runs in the direction from the center to the periphery.

But the wire from sensor B1 will not go outside the machine, so as soon as it is passed from the guide through the plastic of the base and the previously made "U"-shaped cut in the tank, it should be "turned" towards the reed switch, triggered by a permanent magnet located in plastic cover of the machine. The wire is laid next to the wires from this switch and is led to a free bracket (only a network cable passes through it), on which not only the board with parts, but also the T1 transformer is placed. To connect sensor B1, a single-core copper wire in PVC insulation (from a telephone cable) was used. Its inner diameter is 1 mm, and the outer (with insulation) is about 1,5 mm.

Sensor pin B1 is made of a bar of corrosion-resistant steel (08Kh18N10T) with a diameter of 3 mm and a length of 300 mm. The sensor operates on direct current, but it is extremely small (about 40 µA), so electrochemical corrosion can be ignored. The rod is passed through a hole in a rubber plug, with a guide inserted into a cylindrical hole with a diameter of 21 mm with an interference fit. From above, the end of the bar (after a ring of copper wire is soldered to it) is covered with a rubber cap, the outer diameter of which (before assembly) was 22 mm. After that, the upper end of the rod is tinned with "soldering acid" (zinc chloride). A PVC tube is put on the rod, and so that the lower end remains uninsulated from water to a height of about 10 mm. The rod is held in the cork by a tight fit. To prevent the lower end of the sensor from accidentally touching the side wall of the tank, a rubber washer 5 mm thick and 10 mm in diameter is tightly put on it.

Author: V.Bannikov, Moscow

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