# What are all the little resistors for...

R

#### Russ

Jan 1, 1970
0
Real beginerers question: I was looking at a control board for my vending
machine and there are the ususal number of IC's and next to every IC there
are resistors, rows and rows of them. There are also rows of diodes. Why
do they need to add so many resistors to each IC? what do they do? If they
drop the voltage shouldn't they just come in with less voltage and save all
of those resistors? Can someone explain how and why these resistors and
diodes are used in this way?
Thank you very much

B

#### Bob Myers

Jan 1, 1970
0
Russ said:
Real beginerers question: I was looking at a control board for my vending
machine and there are the ususal number of IC's and next to every IC there
are resistors, rows and rows of them. There are also rows of diodes. Why
do they need to add so many resistors to each IC? what do they do? If they
drop the voltage shouldn't they just come in with less voltage and save all
of those resistors? Can someone explain how and why these resistors and
diodes are used in this way?

What you're calling "resistors" are very likely bypass capacitors; these
are used to provide a distributed capacitance across the board, and
one which will respond well to rapid transients, so as to reduce the
effect of noise on the power supply causes by the digital circuits
switching.
On the other hand, there are very often cases in which resistors really
are used in series with the outputs of digital logic ICs, especially when
these outputs are being used to drive long lines or traces. In this case,
the resistors are there for "damping," reducing the amplitude of overshoot,
undershoot, and "ringing" on these lines.

Diodes might be for any of a number of reasons. One possibility is
for protection against electrostatic discharges (ESD).

Bob M.

M

#### me

Jan 1, 1970
0
Real beginerers question: I was looking at a control board for my
vending machine and there are the ususal number of IC's and next to
every IC there are resistors, rows and rows of them. There are also
rows of diodes. Why do they need to add so many resistors to each IC?
what do they do? If they drop the voltage shouldn't they just come in
with less voltage and save all of those resistors? Can someone explain
how and why these resistors and diodes are used in this way?
Thank you very much

resistors and diodes are often used to form circuitry. How they are
connected, to what they are connected, and their values determine the
properties of the circuitry. To sum up the answer, we'd need to know how
they are connected, to what they are connected, and their values to tell
you anything of any value.

(except those who are familiar with the circuitry in question, then they
would just need the machine model number)

B

#### Bob Masta

Jan 1, 1970
0
Real beginerers question: I was looking at a control board for my vending
machine and there are the ususal number of IC's and next to every IC there
are resistors, rows and rows of them. There are also rows of diodes. Why
do they need to add so many resistors to each IC? what do they do? If they
drop the voltage shouldn't they just come in with less voltage and save all
of those resistors? Can someone explain how and why these resistors and
diodes are used in this way?
Thank you very much
Hmm. Since this is from a vending machine, I wonder
if it is the input lines from all the pushbuttons, each
with a pull-up resistor. The diodes might be for some
sort of multiplexing, so that they can be read as rows
and columns by a central processor instead of the
chip needing a dedicated line for each switch.
Just a thought...

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

T

#### TokaMundo

Jan 1, 1970
0
resistors and diodes are often used to form circuitry. How they are
connected, to what they are connected, and their values determine the
properties of the circuitry. To sum up the answer, we'd need to know how
they are connected, to what they are connected, and their values to tell
you anything of any value.

Wow... this could almost be a computer bot response! ;-]

You should be sure to make a few mistakes in spelling or grammar,
such that we know the source is really human! Hehehehe...

Anyway... good job. The short answer... Parts is parts...

K

#### Kitchen Man

Jan 1, 1970
0
Hmm. Since this is from a vending machine, I wonder
if it is the input lines from all the pushbuttons, each
with a pull-up resistor. The diodes might be for some
sort of multiplexing, so that they can be read as rows
and columns by a central processor instead of the
chip needing a dedicated line for each switch.
Just a thought...

My guess is along similar lines. I'm thinking the diodes are zeners,
and the resistors the complementary current control for the zeners.
The total design will take electro-mechanical impulses from coins,
buttons, etc., and convert these to logic levels.

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