C64/C128 Projects

50Hz TOD Timer for C64

This timer is needed when powering C64 with DC (battery or PC power supply).

[fig1: 50Hz timer circuit]


 8,4 : Vcc (+5V)
 6 - Ct
 Ct - gnd
 1 - gnd
 3 - out

Parts List (for 50Hz)

1 NE555 IC
1 2.2uF el. capacitor
2 3.3kOhm resistance


T: period
T=2 x 0.693 x C x R
for 50Hz T=0.02
R x C = 0.01443

if R=6.6K then C=2.2uF ( 6.6x2.2x10^(-3)=0.0145 )

note: It seems to me that something is wrong. Maybe TOD is working with zero-crosses. In this case we should take T=0.01, hence R=3.3K. Trial and error gives the correct answer :)

March 1998
Ilker Ficicilar (İlker Fıçıcılar)

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