Digital timer for the pump. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Digital pump timer

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Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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The process is fully automated, and there is no need to constantly monitor the water level in the tank - the device controls and maintains the specified water level in the tank. The use of a microcontroller made it possible to increase its reliability, as well as to build a small-sized and easily repeatable design.

Digital pump timer
Fig. 1

The timer circuit is shown in fig. 1. The clock frequency of the ATtiny2313 microcontroller (DD1) is set by an external crystal ZQ1. The duration of continuous operation of the pump and the duration of the pause from turning it off to turning it on again is set using two buttons (SB1 and SB2). These values are stored in the non-volatile memory of the microcontroller, so there is no need to re-set them after each power off and then on, which is especially important in rural areas. When the power is restored, the timer starts its work with the formation of a pause, which protects the pump from failure as a result of repeated switching on and off in a short period of time.

Two three-digit seven-element LED indicators with common cathodes (HG1, HG2) during the timer operation show the time remaining until the pump is turned on (while maintaining a pause) or until it is turned off (during water supply). The indication is dynamic. The decoder DD2 with outputs made according to the "open collector" scheme converts the three-digit binary code of the familiarity number generated by the microcontroller into signals applied to the cathodes of the indicators for switching them on one by one. The pump also stops when the maximum level sensor SF1 is triggered. This is accompanied by the display of the inscription FULL on the indicator. The sensor can be any microswitch equipped with a lever with a float. For greater reliability, you can install another microswitch that breaks the timer power circuit if the SF1 sensor does not work for any reason.

Digital pump timer
Fig. 2

All parts of the device, except for the SF1 sensor, are mounted on a printed circuit board made of fiberglass foiled on both sides, shown in Fig. 2. In its author's version, unused sections of the foil on both sides of the board are connected to the -(9 ... 12) V circuit and serve as an additional common wire.

The board is designed for surface mounting parts (except for the ZQ1 quartz resonator, DA1 stabilizer, HG1, HG2 indicators, SB1, SB2 buttons and K1 relay). Relay type - JRC-23F. The resistance of its coil is 167 Ohm, the operating voltage is 5 V. The contacts are designed for switching alternating voltage up to 125 V with a load power of not more than 62,5 VA. A pump or other actuating device, the power of which exceeds the capabilities of this relay, can be turned on using another relay or contactor rated for the appropriate current and voltage. Relay K1 in this case will serve as an intermediate.

Digital pump timer
Fig. 3

The board also has a pin connector XP1, the contacts of which are connected to the microcontroller pins according to the diagram in Fig. 3. It is designed to connect the programmer to the microcontroller already installed on the board. The table shows how the microcontroller configuration bits should be programmed. They set its operation with a quartz resonator with a frequency of more than 8 MHz and delay the start of the program by 16000 cycles. To protect the information in the EEPROM of the microcontroller from accidental damage in the process of increasing the supply voltage, the response threshold of the internal voltage detector (BODLEVEL) is set to 1,8 V.

Digital pump timer

When loading into the program memory of the microcontroller codes from the file Pump-Control.hex available in the application, the duration of the pump and the duration of the pause can be independently changed from 0 to 60 minutes in increments of 1 s.

The timer consumes a current of not more than 9 mA from a voltage source of 12 ... 500 V.

The timer microcontroller program can be downloaded hence.

Author: V. Kuzmenko, R. Chobik, Korsun-Shevchenkovskiy, Ukraine; Publication: radioradar.net

See other articles Section Clocks, timers, relays, load switches.

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