• on Miscellaneous Electronics
  • Published in issue 5/2014 on page 74
About the article

Zero-Electrolytics 555 Timer

The more resistance the better

Zero-Electrolytics 555 Timer
A timer circuit that turns on a pump for a short time every five minutes can be easily made using the famous 555 IC. Unfortunately, it's almost impossible to avoid using electrolytic capacitors to achieve such a long period, which makes the circuit less accurate and reliable, especially in the longer term. However, there is one solution to this problem, and that is to use a special 1 giga-ohm resistor!
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor 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.

R1 = 1GOhm 0.25W 10%; TE Connectivity type RGP0207CHK1G0
R2,R3 = 10MOhm
R4 = 1kOhm
R5 = 10kOhm
C1 = 390nF, lead pitch 5mm or 7.5mm
C2 = 680nF, lead pitch 5mm or 7.5mm
C3 = 100nF, lead pitch 5mm or 7.5mm
D1 = 12V 0.5W zenerdiode
D2 = 1N4007
D3,D4 = 1N4148
T1 = IRF1405ZPBF
IC1 = TLC556CN (DIP14)
K1–K4 = spade terminals, Faston, 0.2’’ pitch
JP1 = 2-pin pinheader, 0.1’’ pitch
S1 = slide switch, miniature, 1 C/O contact; C&K Components type OS102011MA1QN1
S2 = pushbutton with make contact, 12V 50mA, 6x6 mm
F1 = fuse, 10A fast, 5 x 20 mm, with PCB mount 15A holders; 2 pcs Cooper Bussmann type 1A3399-10-R
PCB # 130257-1
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