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Low-cost Heating Controller

Minimum outlay, maximum payback

Low-cost Heating Controller
Before winter gets a grip it’s probably time to give your heating system the once-over. Older boilers are not especially efficient but the cost of replacement is not trivial. The low-cost heating controller presented here measures flow temperature and outdoor temperature to run the boiler more efficiently. Good news for your bank balance and the environment!
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R1 = 100k

R2 = 220 (

R3 = 10k

R4 = 4kΩ7

RN1 = 10-way SIL array 470 ohm

RN2 = 8-way SIL array 100k


C1,C2 = 22pF

C3-C10 = 100nF

C11,C12 = 22µF 20V


D1 = DC-10EWA LED bargraph (Kingbright)

(D2 = SFH506-36, 36kHz IR receiver, Infineon)*

D3 = 1N4001

N1 = MC7805BTE (Fairchild Semiconductor)

IC1 = Atmega32 (Atmel), programmed, Elektor order code 060325-41

IC2 = MAX232CWE (Maxim/Dallas Integrated Products)

(IC3 = DS1820 (Maxim/Dallas Integrated Products)*

IC4 = ULN2803A (e.g. ST, TI, ON)


Q1 =  8MHz quartz crystal, HC-49U case

K2 = relay, 1 nc contact, 12V/2A (e.g. Reichelt # FIN 30.22.9 12V)

S1-S5 = pushbutton, ITT Schadow (Reichelt # DIT 1 XX) (alternative: rotary encoder with push function)

LCD = 2x16 characters, with LSI KS0070B (e.g. Displaytech 162CBCBC from Reichelt) with 14-way SIL connector set

JP1 = boxheader 2x5 pins, angled

JP14 = mono socket, 3.5mm, PCB mount (e.g. Reichelt # ESB35)

S12, S13, S20 = 2-way PCB terminal block, 5mm lead pitch

S21 = 3-way PCB terminal block, 5mm lead pitch

DIL IC sockets, 16-, 18- and 40-way (1 of each)

PCB, order code 060325-1 from www.elektor.com

Suggested parts supplier: www.reichelt.de

External parts

K3,K4 = relay, 1 nc contact, 12V/2A

Rocker switch, on/off

R8,R10 = 1kΩ5

R9,R11 = KTY81/110 (NXP)
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