Need circuit to produce 3 modes of audible confirmation

[Ken Moffett]

Well, a PIC would certainly keep the chip count down! But, you have
the investment of maybe $100.00 for the development system, and the
time it takes to learn the programming language, which, if you're a
programmer, shouldn't be hard at all. And the act of selecting which
PIC you want to use is an exercise in itself.

The only other way that springs to my mind is a pot-load of counters
and logic gates and stuff, which sounds like a dandy exercise for the
reader. ;-)

Good Luck!
Rich

Wrong...wrong...wrong! Google "PicAxe". Free PBasic programming software,
program loads from a serial port directly (through two resistors) to the
chip, and 8 pin chips are cheap (even with shipping from GB). They were
intended for teaching uP's in elementary and high schools, but are great
for real world projects. I have several controlling science displays. These
are "PIC's" with an onboard PBasic interpreters. The 8-pin, 4MHz
PicAxe08/08M will easily do what you described and more.

 

[Jason S]

yup, got it =)

Jason.

 

[Jason S]

You can't let the inputs 1 & 2 "float" since these connect to the logic
NANDs on the output of counter, the logic requires well-defined voltage
levels , either H or L, voltages in between cause them to act up. You have
to put pulldowns to GND there- say 1M ohms- put 1M's right at the input to
the circuit on all IN's for consistency. Where are your inputs coming from
anyway? The diodes are a logic OR and they are in the correct spot.

Ok, yeah I thought the case. I'll ammend my printed copy.
The inputs may or may not be coming from other logic gates, so it's best I
connect the 1M drop-downs I think.

Jason.

 

[Jason S]

Hi Fred,

Thanks so much for the assistance with this.

Your modification below actually worked a lot better than the original (I
decided to go with the modified schematic because I didn't have a CMOS 555
handy). It's working more normally now =) - I am wrapped!
But there's just some very minor issues now that I hope you could sort out
for me...

1. The first beep appears to be longer than the second and third (I know
you mentioned something earlier about a diode, but I didn't quite
understand). I take it that's because the 555 has just come out of a reset?
So as a result, if I connect, say, the 3rd INPUT for three beeps, I hear:
beeeep! beep! beep!

2. With the 10K resistors connected in series and also the 1M drop-downs
for each input like you said, once I disconnect an input (after beeps have
finished), I would hear a very brief 'Blip!' from the buzzer. I actually
thought maybe the 1uF cap had something to do with it, but still does it
even if I remove it.

3. Oh, at power on with an input already connected, it is still beeping 6-9
times. > Not a big issue however. Mainly concerned with the above two.

Kind regards,

Jason.

Hi Fred,

To answer your question, I will be using a self-driven piezo buzzer
which DOES NOT oscillate (I thought that was what I was supposed to
use?), so the 555 will apply power to it when a beep is required (via
the usual resistor/transistor/diode arrangement).

I did a breadboard test of your original schematic this morning, and
it seems to be operating PARTIALLY o.k - Not sure if I did anything
wrong - there's wires everywhere! arrghhh!. There's bit of a problem
that I have encountered....

Problem # 1 : The 555's outpin pin is high if there are no inputs
connected (standby) - isn't it supposed to be low? As soon as I
connect an output, it works o.k but as soon as the input is
disconnected (when the 4017 resets), the 555's output pin goes high
again and stays high (causing the buzzer to sound continuously!).
Not sure what to do here Fred~! I used a logic probe and the NAND
gate that connects to the RST pin of the 4017 intermittently gives
half high half low, and found that the circuit then doesn't 'reset'.
Funny how it's only sometimes.

You are using the bipolar 555 and the typical RST pin current is listed
as 0.1mA, for which the 100K resistors are much too high. If you want to
keep the signal input impedance of the circuit high then you will have
to use the circuit attached below or go to a CMOS 555.

Problem # 2: Also if there is already an input connected BEFORE I
turn the power on to the circuit, buzzer will beep 7, 8 or 9 times
before it stops! i.e. Input 1 = 7 beeps. Input 2 = 8 beeps. Input 3
= 9 beeps. However, the 4017 seems to be going through only 1 cycle
(which is good), because according to the logic probe, each of the
outputs go 'high' only once. Weird.

If live inputs while the circuit is unpowered are a real possibility
then you should put a 10K in series with the input of the NAND driving
the 4017 RST input, and you can add a C+R from VCC to one input of that
NAND for a power on RST if you don't like the beeps.

Let me confirm the following: 1) All gates used are of NAND type
(4011). Note that your text mentioned 'AND'd'!).
Yep-

2) The 4017's CLK/Clock pin is connected to the positive rail at all
times. ???
Yep-

3) Output from the 555 is connected to the CE/Clock Enable pin of
the 4017.
Yep-

4) The inputs - finding that circuit doesn't work properly if any
unused input is 'floating' (i.e. not connected to ground). Are the
diodes in the correct spot?

Either go with a CMOS 555 or use circuit below.

5) What's the deal of not having a square wave for the 555 output?
Does it matter? My output seems pretty square.

It's only personal preference- if you're satisfied with the sound then
go with it.

As I said- either go with CMOS 555 and original circuit, or keep your
bipolar 555 and mod the circuit like shown below. You add a pull-up
resistor from 555 RST to Vcc, the NAND driver for the 4017 RST also drives
the transistor base OR circuit through a 10K and a 10K replaces the 100K
in the other drivers of the base circuit. A power on RC has been added to
RST the 4017 at turn-on. The operation is basically the same except that
now when an IN goes high, it indirectly causes 555 RST high through the
NAND+ transistor combination, instead of directly. The 555 is now RST
after required number of beeps OR when the inputs are removed.
View in a fixed-width font such as Courier.

.
. 5V
. 1U |
. GND--||--+----[100K]-------+
. | |
. .------------------------------------------------------.
. | | _ | |
. | 3x 1N4148 '---| \ [10K] |
. | | o-. | --------- |
. IN 1------[10K]--+-|>|--+---|_/ | +----|RST OUT|----+
. | | | | | | | |
. IN 2------[10K]+-|-|>|--+ | | | 555 | |
. | | | | | | | | |
. IN 3-----------|-|-|>|--+ | | | ASTABLE | BEEPER
. | | | | | | | | |
. | | | [100K] | | | ON TIME | |
. | | | | | | | =BEEP | |
. | | | GND | | | OFF TIME| GND
. | | | | | | 1/2 BEEP|
. | | | | | ---------
. | | | | |
. | | | | |
. | | '--------. | |
. | '--------. | | |
. | | | | |
. .---------------------------+-[10K]--------.
. | | | | | |
. | | --4017-- | | | |
. | | | Q0| | | \| |
. | | |-- | | | 2N3904|---+
. | '---|CE | | | <| |
. | | | | | _ 4011 | |
. | '1'-|CLK Q1|--------| \ GND |
. | | | | | | o _ |
. | | | | '--|_/ '-| \ |
. | | | | _ | o--[10K]--+
. | | Q2|--------| \ .-|_/ |
. | | | | | o' |
. | | | '----|_/ |
. | | | |
. | | Q3|--------------------[10K]--'
. | | |
. '-----|RST . |
. | |
. | Q9|
. | |
. --------

 

[Jason S]

3. Oh, at power on with an input already connected, it is still beeping
6-9 times. > Not a big issue however. Mainly concerned with the above
two.

Actually forget number 3 (above). It's working fine at startup now.

 

[Fred Bloggs]

Hi Fred,

Thanks so much for the assistance with this.

Your modification below actually worked a lot better than the original (I
decided to go with the modified schematic because I didn't have a CMOS 555
handy). It's working more normally now =) - I am wrapped!
But there's just some very minor issues now that I hope you could sort out
for me...

1. The first beep appears to be longer than the second and third (I know
you mentioned something earlier about a diode, but I didn't quite
understand). I take it that's because the 555 has just come out of a reset?
So as a result, if I connect, say, the 3rd INPUT for three beeps, I hear:
beeeep! beep! beep!

Right- the 555 pin 5 ,CONT, is the first node of an internal R-R-R
voltage divider to GND which is the threshold for the THRESH switch
point, and 1/2 the CONT voltage is the threshold for the TRIG switch
point. By connecting a small diode from CONT to OUT with anode at CONT,
when OUT is high, the diode is back biased and does not affect the trip
point for THRESH, but when OUT is low, which means the timing capacitor
is being discharged downwards towards the TRIG threshold, the diode
pulls the internal CONT node down to 0.7V making the new TRIG threshold
~0.35V. In your application, when you remove RST, the first beep lasts
for the time it takes the timing capacitor to charge from 0 to THRESH
threshold of 2 x Vcc/3, then goes off for the time it takes to discharge
to 0.35V, then back on for the time it takes to re-charge from 0.35V to
THRESH threshold, then off for time to discharge back 0.35V, etc...All
the ON times are about the same for practical purposes this way. Without
the diode the second and third on times would be of duration the time it
takes to charge from 1/3 Vcc to 2/3 Vcc- and they sound noticeably
shorter than the first beep.

2. With the 10K resistors connected in series and also the 1M drop-downs
for each input like you said, once I disconnect an input (after beeps have
finished), I would hear a very brief 'Blip!' from the buzzer. I actually
thought maybe the 1uF cap had something to do with it, but still does it
even if I remove it.

When a last input is removed, the input NAND gate RSTs the 4017 and
drives the base of the 2N3904 all at the same time. The RST of the 4017
removes its base drive from the transistor tending to turn it off while
the NAND is applying its drive turning it ON. The NAND base drive part
should be solidly on several hundred nanoseconds before the 4017 outputs
begin to remove their base drive so that I am at a loss to explain why
you are hearing a blip. If you are manually removing a clip lead or
using a switch, which has bounce at turn-off, then an intermittent
disconnect-connect-disconnect etc jittering of the input contact,
however brief, may be causing the blip you are hearing. You can
eliminate the effect, for reasonable jitter of input connection times,
by adding a filter capacitor from collector to base of the 2N3904. This
will make the transistor have a fast on- slow-off characteristic and
help prevent the blip. A schematic with all the changes:

View in a fixed-width font such as Courier.

..
.. 5V
.. 1U |
.. GND----||--+----[100K]----+---------.
.. | | |
.. [10K] 10K] |
.. | | |
.. .-----------------------------------------------------.
.. | | _ | | |
.. | 3x 1N4148 '---| \ | | |
.. | | o-. | --------- |
..IN1----+----[10K]---+-|>|--+---|_/ | +----|RST OUT|--+---+
.. | | | | | | | | | |
..IN2--+------[10K]-+-|-|>|--+ | | | 555 | | |
.. | | | | | | | | | OSC | | |
..IN3+--------[10K]-|-|-|>|--+ | | | | | BEEPER
.. | | | | | | | | | | | | |
.. 1M | | | | | [100K] | | | | | |
.. | | | | | | | | | .-|CONT | | |
.. |1M | | | | GND | | | | | | GND
.. | | | | | | | | | | | |
.. | |1M | | | | | | --------- |
.. | | | | | | | | | | |
.. | | | | | | | | | gnd |
.. '-+-' | | '--------. | | | |
.. | | '--------. | | | '-----|>|------'
.. GND | | | | |
.. .---------------------------' | +
.. | | | | +----||--.
.. | | --4017-- | | | 1U |
.. | | | Q0| | | \| |
.. | | |-- | | | 2N3904 |------+
.. | '---|CE | | | <| |
.. | | | | | _ 4011 | |
.. | '1'-|CLK Q1|--------| \ GND |
.. | | | | | | o _ |
.. | | | | '--|_/ '-| \ |
.. | | | | _ | o--[10K]--+
.. | | Q2|--------| \ .-|_/ |
.. | | | | | o' |
.. | | | '----|_/ |
.. | | | |
.. | | Q3|--------------------[10K]--+
.. | | | |
.. +-----|RST . | |
.. | | | |
.. | | Q9| |
.. | | | .-----------[10K]--'
.. | -------- |
.. | |
.. '-----------------------'
..
..
..

 

[Jason S]

Fred,

It works! Hooray! Thank you so so much. You have been great.

The diode worked very well to fix the longer beep problem -thank you-, but
as with the cap to fix the 'blips' - it failed miserably... actually made it
worse. So I left it as it was, but connected a transistor to each input and
works a lot better now.

Appreciate your help.

Regards,

Jason.

Hi Fred,

Thanks so much for the assistance with this.

Your modification below actually worked a lot better than the original (I
decided to go with the modified schematic because I didn't have a CMOS
555 handy). It's working more normally now =) - I am wrapped!
But there's just some very minor issues now that I hope you could sort
out for me...

1. The first beep appears to be longer than the second and third (I know
you mentioned something earlier about a diode, but I didn't quite
understand). I take it that's because the 555 has just come out of a
reset? So as a result, if I connect, say, the 3rd INPUT for three beeps,
I hear: beeeep! beep! beep!

Right- the 555 pin 5 ,CONT, is the first node of an internal R-R-R voltage
divider to GND which is the threshold for the THRESH switch point, and 1/2
the CONT voltage is the threshold for the TRIG switch point. By connecting
a small diode from CONT to OUT with anode at CONT, when OUT is high, the
diode is back biased and does not affect the trip point for THRESH, but
when OUT is low, which means the timing capacitor is being discharged
downwards towards the TRIG threshold, the diode pulls the internal CONT
node down to 0.7V making the new TRIG threshold ~0.35V. In your
application, when you remove RST, the first beep lasts for the time it
takes the timing capacitor to charge from 0 to THRESH threshold of 2 x
Vcc/3, then goes off for the time it takes to discharge to 0.35V, then
back on for the time it takes to re-charge from 0.35V to THRESH threshold,
then off for time to discharge back 0.35V, etc...All the ON times are
about the same for practical purposes this way. Without the diode the
second and third on times would be of duration the time it takes to charge
from 1/3 Vcc to 2/3 Vcc- and they sound noticeably shorter than the first
beep.

2. With the 10K resistors connected in series and also the 1M drop-downs
for each input like you said, once I disconnect an input (after beeps
have finished), I would hear a very brief 'Blip!' from the buzzer. I
actually thought maybe the 1uF cap had something to do with it, but still
does it even if I remove it.

When a last input is removed, the input NAND gate RSTs the 4017 and drives
the base of the 2N3904 all at the same time. The RST of the 4017 removes
its base drive from the transistor tending to turn it off while the NAND
is applying its drive turning it ON. The NAND base drive part should be
solidly on several hundred nanoseconds before the 4017 outputs begin to
remove their base drive so that I am at a loss to explain why you are
hearing a blip. If you are manually removing a clip lead or using a
switch, which has bounce at turn-off, then an intermittent
disconnect-connect-disconnect etc jittering of the input contact, however
brief, may be causing the blip you are hearing. You can eliminate the
effect, for reasonable jitter of input connection times, by adding a
filter capacitor from collector to base of the 2N3904. This will make the
transistor have a fast on- slow-off characteristic and help prevent the
blip. A schematic with all the changes:

View in a fixed-width font such as Courier.

.
. 5V
. 1U |
. GND----||--+----[100K]----+---------.
. | | |
. [10K] 10K] |
. | | |
. .-----------------------------------------------------.
. | | _ | | |
. | 3x 1N4148 '---| \ | | |
. | | o-. | --------- |
.IN1----+----[10K]---+-|>|--+---|_/ | +----|RST OUT|--+---+
. | | | | | | | | | |
.IN2--+------[10K]-+-|-|>|--+ | | | 555 | | |
. | | | | | | | | | OSC | | |
.IN3+--------[10K]-|-|-|>|--+ | | | | | BEEPER
. | | | | | | | | | | | | |
. 1M | | | | | [100K] | | | | | |
. | | | | | | | | | .-|CONT | | |
. |1M | | | | GND | | | | | | GND
. | | | | | | | | | | | |
. | |1M | | | | | | --------- |
. | | | | | | | | | | |
. | | | | | | | | | gnd |
. '-+-' | | '--------. | | | |
. | | '--------. | | | '-----|>|------'
. GND | | | | |
. .---------------------------' | +
. | | | | +----||--.
. | | --4017-- | | | 1U |
. | | | Q0| | | \| |
. | | |-- | | | 2N3904 |------+
. | '---|CE | | | <| |
. | | | | | _ 4011 | |
. | '1'-|CLK Q1|--------| \ GND |
. | | | | | | o _ |
. | | | | '--|_/ '-| \ |
. | | | | _ | o--[10K]--+
. | | Q2|--------| \ .-|_/ |
. | | | | | o' |
. | | | '----|_/ |
. | | | |
. | | Q3|--------------------[10K]--+
. | | | |
. +-----|RST . | |
. | | | |
. | | Q9| |
. | | | .-----------[10K]--'
. | -------- |
. | |
. '-----------------------'
.
.
.