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HANDS-ON HOME & GARDEN Go with the Fl F Jürgen Maiß In this day and age enjoying constant hot water should not be an expensive luxury. All the same, the way some households squander energy to provide this on tap makes you wonder. Our novel circuit saves both your bank balance and the environment! The circulation pump in a heating system is the device that makes possible the accustomed luxury of having hot water at the turn of the tap. Unavoidable heat losses in the plumbing system and the constant operation of the circulation pump lead to profligate waste of energy, however. In fact, according to Oxford University’s Environmental Change Institute, the pump consumes as much energy as lighting or the fridge in most households, and a pan-European drive is now underway to find ways of saving costs for what is one of the most ignored electrical devices in the home. To cut power consumption we need to lag all pipes well and reduce the amount of time that the pump operates to only when hot water is actually required. There are already a variety of control systems on the market for managing circulation pumps. One of these relies on flow sensors, which react adequately fast but are hardly simple to install (they require plumbing into the pipe system). Other devices observe 42 temperature variations. These determine the temperature difference between the hot water and circulation pipes, using any variation from the desired value as the trigger. The systems are both reliable and very simple to install, since no ‘invasive action’ is necessary to the plumbing. Unfortunately the sluggish action of the temperature sensors means they do not operate very rapidly. One feature that both systems share is their relatively high purchase cost. Our approach here takes a rather different route. A simple, readily available piezo sounder used as an acoustic emission sensor detects the sound of flowing water in the plumbing system. This is what we use as the switching trigger. Piezoelectric effect Piezoelectric sounders, also known as electronic buzzers, are used in many electronic circuits as audible transducers or ‘bleepers’. Easy to use, they also take up little space and are extremely affordable. A change in the voltage
ow SENSOR C1 47n 12/2006 - elektor electronics R1 100k 100k R2 1k R3 1M R6 100k 3 7 IC1 6 C3 3 7 2 4 10n 2 IC2 LTC1049 R4 P1 100k C2 100n 10k C4 Piezoelectric transducer controls domestic water system 4 LTC1049 R5 100n applied to the piezo crystal in the sounder deforms it slightly, an effect that is used to generate sound. The principle is reversible too, enabling the transducer to work as a highly sensitive ‘microphone’ as well. The variations in voltage charge resulting from altered mechanical stress on the crystal structure can be registered electronically and processed further. Piezoelectric sensors are widely used today in workshop tools, for automotive applications and in technical setups as pressure, power and dynamic accelerometer devices. The pump control system shown in Figure 1 comprises several modules, each with their own function. • The first is a preamplifier stage with an amplification factor of from 10 to 1,000. The signal coming from the sensor has a value in the region of 100 to 300 µV and is delivered via coupling capacitor C1 to the non-inverting input of IC1. The amplification of this stage is set by trimpot P1. The 6 C5 10n 1M R7 51k 5k6 R8 3 2 IC3 7 4 LTC1049 R15 P2 20k 6 C6 1µ C7 33n 100k 6 VCC 1 FIN SWIN 5 IC4 R LM2907 RC GND 4 7 2 C 3 R12 +9V...+12V D4 78L05 +5V 1N4007 C11 10µ 25V C10 100n IC5 C9 100n C8 1µ VSS 8 R13 30k 10k 5k1 5k1 Figure 1. The pump control comprises five capacitor-coupled stages. R17 extremely low-noise precision amplifier LTC1049 (from Linear Technology) functions not only as an amplifier but also as an impedance adapter with a high-Z input resistor to avoid loading the sensor signal. Coupling capacitor C3 takes the now boosted sensor signal to a second amplifier (once more type LTC1049 with an amplification factor of 10). Total amplification is defined as A = [(R3 / (R4+P1)) +1] x [(R6 / R5) +1]. • The signal, now amplified to around 1.0 V is fed via C5 to a comparator stage. The switching threshold for IC3 (yet again a LTC1049) is set in the region of around 0.5 to 1.55 V by R8, R15 and trimpot P2. If the sensor detects a flow signal, a squarewave output voltage of approximately 1 kHz appears at the output of IC3. • This squarewave signal is taken via C6 to the frequency-to-voltage converter LM2907 (IC4). This module operates in ‘speed switch-mode’ and above the frequency set as f = 1 / (2 R9 R10 10k IC6 2 GP5/CIN GP4/COUT 3 4 GP3/MC GP2 5 GP1 6 GP0 7 R11 1 8 PIC12C675P R16 10k DETECT C7R12) delivers a High output level, which — • provides the trigger signal for the PIC16F675 microcontroller that follows. As each of the switching elements is connected by coupling capacitors, they can all be modified easily for other applications too. The amplifier circuitry would, for instance, make a magnificent microphone amplifier, ultrasonic amplifier or ground motion detector (geophone). Linear Technology provides for its own modules a free and easy-to-use simulation tool called SwitcherCadIII. A simulation program for this project is contained in our Project Software archive file 060099-11.zip which can be downloaded free of charge from www.elektor.com. Soft- and hardware The software controlling the pump is relatively straightforward; the program can be modified according to requirements and the particular circuit appli- D3 PUMP ON SCAN D2 D1 D6 BC550 1k 060099 - 11 R14 +5V RE1 T1 M M1 P 230V N 43
Page 1 and 2: free supplement Tune that dial shor
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Page 25 and 26: ture becomes 180 MHz. Normally the
Page 27 and 28: lated signal with exactly the same
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