Re: weightlifting score lights
- I've posted a schematic for a simple scoring circuit that uses 4 ICs
a small relay and a few resistors. You'll find it in the "Files"
section under "scoring_circuit.pdf".
It makes use of 3 CMOS ICs and one transistor array to handle output
current. CMOS devices use very little current (microamperes), are
easy to obtain, work over a wide variety of voltages (usually about 5
to 18 volts) and easy to design with.
Each judge's station is the same, two momentary contact switches that
connect to an XOR gate (exclusive OR). If neither or both switches
are depressed, the gate is at 0 (negative). Only if one switch is
depressed (pass or fail) does the gate become 1 (positive). The
output of the XOR gate for each judge (Note: in my schematic I've
drawn only one judge's station, the other two are the same) is
connected one of the input of a 4 input NAND (NOT AND) gate of a 4012
IC. Since there are three judges, connect the 4th input to the
positive voltage through a 10k resistor to hold it at a logical 1.
This gate will output a 1 (positive voltage) until all inputs are 1
when the output will go to 0 (negative voltage). This only occurs
when all the judges have depressed one and only one switch. The
second 4 input NAND of the 4012 is used to invert the signal of the
first (Note: this may seem odd, but I've found it easier to get NAND
CMOS ICs compared with AND CMOS ICs). The output is sent to one of
the transistors on the ULN2803 array to increase the output to
operate a small relay. This relay supplies the +ve voltage to the
The outputs of the "fail" switches go to a 4042 Quad Transparent
Latch which has two outputs for each input (one inverted, one non-
inverted). Only one line is needed since it is either a "fail"
(positve) or a "pass" (negative) situation. In this particular
circuit, the latching function is not used so the judges may change
their scores at any time, however, if desired the 4042 can be latched
to lock in the scores (you should be able to figure out a simple way
by studying the data sheets). Both clock and polarity are grounded.
Use inputs D1 to D3 for the judges, ground input D0. Connect Q1 to Q3
and the inverted outputs Q1 to Q3 to the transistors in the ULN2803.
These control the lights. The advantage of the ULN2803 is that it is
designed for use with CMOS logic and doesn't require any resistors to
For lights use high output LEDs with current limiting resistors
depending upon your working voltages. If you would like to use mains
operated lights, use opto-isolators and triacs to isolate this
Data sheets for the CD4042 and ULN2803 are located in the "Files"
section along with my hand-drawn schematic. You'll need the following
6 momentary contact switches (SPST)
6 100k ohm resistors (eighth or quarter watt)
7 10k ohm resistors (eighth or quarter watt)
1 CD4070 Quad XOR
1 CD4012 Dual 4-input NAND
1 CD4042 Quad transparent latch
1 ULN2803 Octal high voltage, high current darlington transistor array
1 Low voltage relay (you can find these on computer modem boards)
Check out your local suppliers for high-output LEDs, these are really
bright and if used with the proper reflectors should be of sufficient
--- In email@example.com, "stuart hamilton"
> This will probably be an easy problem for you guys to solve, but Iindicate
> need some help. I help run the Colchester Weight Lifting Club in
> Colchester, UK, and we need to make or have made a set of score
> lights for our Weight Lifting competitions.
> The way they need to work is as follows:
> There are three referees, each of them has a switch box in their
> hands with two switches/buttons, one red and one white.
> In front of the audience is a box with two rows of lights, a row of
> three white lights and a row of three red lights. After each lift
> each referee pushes either a red button or a white button to
> whether it was a pass (white) or a fail (red).This
> The full set of lights should not come on untill the centre referee
> (the head ref) makes his choice and pushes his choice of button.
> stops any of the referees making their choice of pass or fail afterie
> they have seen the decision of the other referees.
> When the decision has been seen and recorded the centre referee
> removes his finger from the button and all the lights go out and we
> are ready to go for the next lift.
> What I would like to know is the circuit diagram that I need to use
> to make this score light set. I want to be able to use low voltage
> around 6v, 9v or 12v with power supplied by a/some battery/ies so
> that we don't need mains supply or thick cables.
> Can anyone help
> Thanking you in advance
> Stuart Hamilton
> Colchester Weight Lifting Club
> Colchester, UK
- I've added a circuit modification for locking in the scores, you can
find this in the "Files" section of this group. What it does is to
use the output of the XOR of the head judge to latch the latches in
the 4042. Since the latches are loaded with data directly from the
switches and the latching signal has to travel through 2 additional
gates (the judge's XOR and an XOR gate on the 4042) this should delay
the latching enough so that the main judge's decision can be
captured. I didn't bother to include any switch debouncing since this
circuit is very slow. I have, however, suggested in the text file
that accompanies the schematic that if capturing the judge's decision
is a a problem that a delay can be fashioned from the "left-over" XOR
gate to delay the latching by a small amount.
Please take a look at the schematic and see if it looks okay.