v 20060906 1
C 1200 86000 1 0 0 lm555-1.sym
{
T 3000 86000 5 10 1 1 0 0 1
refdes=U4
}
N 2000 88800 2000 89100 4
N 2000 89100 2800 89100 4
N 2800 89100 2800 88800 4
N 2400 89300 2400 89100 4
C 2200 89300 1 0 0 vcc-1.sym
C 8400 87400 1 0 0 resistor-1.sym
{
T 9200 87300 5 10 1 1 180 0 1
refdes=R1
}
C 4700 87800 1 270 0 resistor-1.sym
{
T 4600 87000 5 10 1 1 90 0 1
refdes=R2
}
C 4600 86100 1 270 0 capacitor-1.sym
{
T 4600 85200 5 10 1 1 90 0 1
refdes=C1
T 5200 85200 5 10 1 1 90 0 1
value=0.1uF
}
N 4800 88000 4800 87800 4
N 4800 86900 4800 86100 4
N 4800 85200 4800 85000 4
C 4700 84700 1 0 0 gnd-1.sym
N 3500 87900 4800 87900 4
N 3500 87500 4400 87500 4
N 4400 85700 4400 87500 4
N 4400 86800 4800 86800 4
N 1200 87500 600 87500 4
N 600 87500 600 85700 4
N 600 85700 4400 85700 4
N 1200 86400 1100 86400 4
N 1100 86400 1100 86300 4
C 1000 86000 1 0 0 gnd-1.sym
N 4800 89100 4800 88900 4
C 4600 89100 1 0 0 vcc-1.sym
N 3500 86400 5700 86400 4
C 9200 74900 1 0 0 cvstitleblock-1.sym
{
T 9800 75300 5 10 1 1 0 0 1
date=2006-11-07
T 13700 75300 5 10 0 1 0 0 1
rev=
T 15200 75000 5 10 1 1 0 0 1
auth=Tom Quetchenbach
T 10000 75600 5 10 0 1 0 0 1
fname=
T 13000 76000 5 14 1 1 0 4 1
title=Pumpkin Drop Circuits
}
T 500 84500 9 10 1 0 0 0 4
This is the basic 555 astable configuration.
For 50% duty cycle, make R1 1K. Then
the frequency is 1.44/((1K + 2 * R2)*C.
See http://tinyurl.com/ym8qtq
T 500 89900 9 10 1 0 0 0 2
Connect the output to one of the other
circuits shown here, or something else.
C 5700 86300 1 0 0 output-1.sym
{
T 5800 86600 5 10 0 0 0 0 1
device=OUTPUT
T 5900 86600 5 10 1 1 0 0 1
netname=CLK
}
T 7300 89900 9 10 1 0 0 0 2
Case 1: One set of LEDs flashing on
and off. This is a piece of cake:
C 9800 87000 1 0 0 npn-1.sym
{
T 10400 87500 5 10 0 0 0 0 1
device=NPN_TRANSISTOR
T 10400 87500 5 10 1 1 0 0 1
refdes=Q1
}
N 8400 87500 8100 87500 4
C 7300 87400 1 0 0 input-1.sym
{
T 7300 87700 5 10 0 0 0 0 1
device=INPUT
T 7300 87700 5 10 1 1 0 0 1
netname=CLK
}
N 9300 87500 9800 87500 4
N 10300 87000 10300 86700 4
N 10300 88400 10300 88000 4
C 10200 86400 1 0 0 gnd-1.sym
C 4700 88900 1 270 0 resistor-1.sym
{
T 4600 88100 5 10 1 1 90 0 1
refdes=R1
}
C 10200 89300 1 270 0 resistor-1.sym
{
T 10100 88500 5 10 1 1 90 0 1
refdes=R2
}
N 10300 89300 10300 89600 4
N 10300 89600 10600 89600 4
T 7000 84700 9 10 1 0 0 0 9
R1 should be about 1K; you may not
need R2 at all. For a 4.5-volt supply,
hfe * 2.2V/R1 = Ic (roughly)
where hfe for most transistors is on the
order of 100 and Ic is the current you
want to see at the collector.

You can determine a good
value for R1 by experimenting.
T 12200 90100 9 10 1 0 0 0 1
Case 2: two sets of LEDs alternating.
C 13000 87500 1 0 0 resistor-1.sym
{
T 13800 87400 5 10 1 1 180 0 1
refdes=R1
}
C 14400 87100 1 0 0 npn-1.sym
{
T 15000 87600 5 10 0 0 0 0 1
device=NPN_TRANSISTOR
T 15000 87600 5 10 1 1 0 0 1
refdes=Q1
}
N 13000 87600 12700 87600 4
C 11900 87500 1 0 0 input-1.sym
{
T 11900 87800 5 10 0 0 0 0 1
device=INPUT
T 11900 87800 5 10 1 1 0 0 1
netname=CLK
}
N 13900 87600 14400 87600 4
N 14900 87100 14900 86800 4
N 14900 88500 14900 88100 4
C 14800 86500 1 0 0 gnd-1.sym
C 14800 89400 1 270 0 resistor-1.sym
{
T 14700 88600 5 10 1 1 90 0 1
refdes=R2
}
T 10700 89500 9 10 1 0 0 0 1
LED -
C 13100 83600 1 0 0 resistor-1.sym
{
T 13900 83500 5 10 1 1 180 0 1
refdes=R3
T 13100 83400 5 10 1 1 0 0 1
value=1K
}
C 14500 83200 1 0 0 npn-1.sym
{
T 15100 83700 5 10 0 0 0 0 1
device=NPN_TRANSISTOR
T 15100 83700 5 10 1 1 0 0 1
refdes=Q2
}
N 14000 83700 14500 83700 4
N 15000 83200 15000 82900 4
N 15000 84600 15000 84200 4
C 14900 82600 1 0 0 gnd-1.sym
C 14900 85500 1 270 0 resistor-1.sym
{
T 14800 84700 5 10 1 1 90 0 1
refdes=R4
}
N 15000 85500 15000 85800 4
C 14800 85800 1 0 0 vcc-1.sym
N 14900 89400 14900 89700 4
N 14900 89700 15200 89700 4
T 15300 89600 9 10 1 0 0 0 1
LED 1-
N 12800 87600 12800 83700 4
N 12800 83700 13100 83700 4
C 17500 83200 1 0 0 npn-1.sym
{
T 18100 83700 5 10 0 0 0 0 1
device=NPN_TRANSISTOR
T 18100 83700 5 10 1 1 0 0 1
refdes=Q3
}
N 18000 83200 18000 82900 4
N 18000 84600 18000 84200 4
C 17900 82600 1 0 0 gnd-1.sym
C 17900 85500 1 270 0 resistor-1.sym
{
T 17800 84700 5 10 1 1 90 0 1
refdes=R6
}
N 16100 83700 15800 83700 4
N 15800 83700 15800 84400 4
N 15800 84400 15000 84400 4
N 18000 85500 18000 85800 4
N 18000 85800 18300 85800 4
T 18400 85700 9 10 1 0 0 0 1
LED 2-
T 15600 86900 9 10 1 0 0 0 4
Probably R1 = 1K, R4 = 1K,
R5 = 100; adjust as necessary.
I haven't tested these values.

C 16100 83600 1 0 0 resistor-1.sym
{
T 16900 83500 5 10 1 1 180 0 1
refdes=R5
}
N 17000 83700 17500 83700 4
T 7800 82000 9 10 1 0 0 0 7
In these circuits, the transistors that drive
LEDs need to be able to handle moderately
high collector currents, on the order of half
an amp. The 2N3904 (Ic=200mA) will not
do; a 2N2222 will work fine. You can even
use a 2N3055 (the prac phys transistor) or
a TIP29C or some other power transistor.
T 1900 81800 9 10 1 0 0 0 2
Case 3: more than two sets of LEDs
lighting up in sequence
C 6100 77800 1 0 0 ULN2801A-1.sym
{
T 6400 81100 5 10 1 1 0 0 1
refdes=U2
T 6400 81500 5 10 0 0 0 0 1
device=ULN2803
}
C 2000 76200 1 0 0 4017-2.sym
{
T 3700 80900 5 10 1 1 0 6 1
refdes=U1
T 2300 81050 5 10 0 0 0 0 1
device=4017
T 2300 81250 5 10 0 0 0 0 1
footprint=DIP16
}
N 4000 80500 6100 80500 4
N 4000 80100 4400 80100 4
N 4400 80100 4400 80200 4
N 4400 80200 6100 80200 4
N 4000 79700 4500 79700 4
N 4500 79700 4500 79900 4
N 4500 79900 6100 79900 4
N 4000 79300 4700 79300 4
N 4700 79300 4700 79600 4
N 4700 79600 6100 79600 4
N 4000 78900 4400 78900 4
N 4400 78900 4400 75900 4
N 4400 75900 2000 75900 4
N 2000 75900 2000 76500 4
N 2000 76900 1500 76900 4
N 1500 76900 1500 76600 4
N 7300 77800 7300 77500 4
C 1400 76300 1 0 0 gnd-1.sym
C 7200 77200 1 0 0 gnd-1.sym
N 8500 80500 9600 80500 4
C 9600 80400 1 0 0 resistor-1.sym
{
T 10400 80800 5 10 1 1 180 0 1
refdes=R1
}
N 8500 80200 10800 80200 4
C 10800 80100 1 0 0 resistor-1.sym
{
T 11600 80500 5 10 1 1 180 0 1
refdes=R2
}
N 8500 79900 12000 79900 4
C 12000 79800 1 0 0 resistor-1.sym
{
T 12800 80200 5 10 1 1 180 0 1
refdes=R3
}
N 8500 79600 13200 79600 4
C 13200 79500 1 0 0 resistor-1.sym
{
T 14000 79900 5 10 1 1 180 0 1
refdes=R4
}
N 10500 80500 10500 80800 4
N 10500 80800 10800 80800 4
T 10900 80700 9 10 1 0 0 0 1
LED 1-
N 11700 80200 11700 80500 4
N 11700 80500 12000 80500 4
T 12100 80400 9 10 1 0 0 0 1
LED 2-
N 12900 79900 12900 80200 4
N 12900 80200 13200 80200 4
T 13300 80100 9 10 1 0 0 0 1
LED 3-
N 14100 79600 14100 79900 4
N 14100 79900 14400 79900 4
T 14500 79800 9 10 1 0 0 0 1
LED 4-
T 9200 79300 9 10 1 0 0 2 9
As with the other circuits, you may be able
to get away with omitting the resistors.

Instead of a ULN2801, you can use a
ULN2803; gschem doesn't have a symbol
for this chip.

Nothing gets connected to pin 10 of the
ULN2803.
N 2000 78500 1700 78500 4
C 900 78400 1 0 0 input-1.sym
{
T 900 78700 5 10 0 0 0 0 1
device=INPUT
T 900 78700 5 10 1 1 0 0 1
netname=CLK
}
T 4900 74800 9 10 1 0 0 0 9
If you're using N sets of LEDs, where N < 10,
connect the N+1 output to the reset pin. If
N = 10, connect the reset pin to ground.
Here, N = 4.

Be careful with the pin numbering on
the 4017. The numbers on the
OUTSIDE of the box in the diagram
are the pin numbers.
B 7700 81900 3900 1900 3 0 0 0 -1 -1 0 -1 -1 -1 -1 -1
T 13400 78600 9 10 1 0 0 0 3
The ULN2803 is actually just an array of NPN
transistors in a chip, so you can use discrete
transistors, as in Case 1, if you want.