Burkhard Kainka
About the article

Relaxation Machine

A servo-powered pendulum

Relaxation Machine
It is a generally known and accepted fact that servos used in radiocontrolled models see very little or no use outside the model flying, racing or boating season. A pity, considering these devices can be used for many useful tasks…For example, a servo that’s not used anyway could be attached to a large pendulum of which the smooth and steady motion may help people relax and even fall asleep. For this (psychological) effect to be achieved the movement has to be sine-shaped like that of a real and very long pendulum.The small circuit of the Relaxation Machine you find in Figure 1 consists of two parts. A pulse generator based on a 555 supplies positive pulses with a length between 1 and 2 ms (‘mark’) and a pause of 20 ms (‘space’), representing a typical servo control signal. In addition there’s a sinewave generator designed to supply a very low frequency of about 0.25 Hz which corresponds to one full period in four seconds. The sinewave generator employs a phase shifting network and supplies a sinewave with very low distortion. If you want to lengthen the period, simply increase the value of C1, C2 and C3 a little.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1 = 15kOhm
R2,R3,R4 = 100kOhm
R5, R8 = 1kOhm
R6 = 10kOhm
R7 = 220 kOhm
P1 = 10kOhm preset
C1,C2,C3 = 22µ F 10V
C4, C6 = 220µ F 10V
C5 = 100nF
D1 = 1N4148
T1, T2 = BC 549C
IC1 = 555C or 7555 (CMOS)
K1 = 3-way pinheader
2 solder pins
PCB, available from The PCBShop
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