looking for a 555 timer circuit

[Wayne]

I'm getting ready to build this, and I was going over the schematic. I
don't understand something: how does it get powered? I see where one
side of S1 (which I'm assuming is NO) is connected to VCC, but see no
others. Is S1 normally closed, or am I missing something obvious?

Thanks

 

[John Fields]

I'm getting ready to build this, and I was going over the schematic. I
don't understand something: how does it get powered? I see where one
side of S1 (which I'm assuming is NO) is connected to VCC, but see no
others. Is S1 normally closed, or am I missing something obvious?

No, S1 _is_ normally open and, by convention, (since it's common
knowledge and available on the data sheets) we usually don't show
the power connections, or we tabulate them on the drawing. Guess I
should have made a table!

Anyway, here it is:

+5V 0V
REF TYPE Vcc GND
PIN PIN
-------+------+-----+-----
U1 7555 8 1
U2 HC175 14 7
U3 HC02 14 7
U4 HC4060 16 8

Also not shown are the 0.1µF bypass capacitors that it's considered
"good practice" to install between Vcc and ground on each chip.
Cheap ceramics are fine.

 

[Wayne]

I've built the circuit and I'm testing it now. Right now, all three
outputs are high and stay high (>2V) until I press the reset button, at
which time they all go low. I haven't waited the 30+ minutes yet after
resetting to see what would happen. I've double-checked all of my
connections and made sure I have what is shown in revB plus the changes
you mentioned earlier. I'm using a 5V DV power supply.

 

[Wayne]

I'm looking at the data sheet for the 4060, and it's not matching what
you have in the schematic: Q11 doesn't exist on the data sheet (I've
looked at 3), and Q6 is on pin 4, not 6. I'm trying to figure out how
the 4060 works, but haven't yet. What should Q11 actually be?

 

[John Fields]

I've built the circuit and I'm testing it now. Right now, all three
outputs are high and stay high (>2V) until I press the reset button, at
which time they all go low. I haven't waited the 30+ minutes yet after
resetting to see what would happen. I've double-checked all of my
connections and made sure I have what is shown in revB plus the changes
you mentioned earlier. I'm using a 5V DV power supply.

---
Did you make the changes I outlined in my last post:


"In going over the circuit for the last time, (LOL) I found a few
errors:

1. U2-5 should be connected to U1-3, not U1-1

2. C1 should be an 0.18µF polyester cap.

3. R1 should be a standard 2 megohm +/- 5% 1/4W carbon film
resistor."?


In either case, it should be working, but if you didn't make the
changes the timing will be off.

I don't understand whether you're saying that it doesn't work at
all, or whether you're saying that you don't know whether it's
working properly because you haven't waited the half-hour or so to
make sure whether it's working or not.

In any case, to start troubleshooting it, disconnect it from the DC
supply and disconnect all of the loads. Then set R2 to its halfway
point and reconnect the supply. You should see a 5VDC square wave
with a period of 1/2 s (2Hz) on U1-7.

If that works, then the oscillator and the first three stages of the
internal divider chain in the 4060 are working. If it isn't, then
there's a wiring error or a bad chip somewhere. Also, if you press
the PAUSE switch, all of U1's outputs should go low for as long as
the switch is pressed. After it's released, pin 7 should toggle at
2Hz.

Try it and post back with what you find and what kind of test
equipment you have available, and we can devise a troubleshooting
plan.

BTW, if U3 comes up with the outputs all high, (which is entirely
possible and doesn't indicate an error of any kind) that means that
all three pumps will run at the same time for 30 seconds when you
first power up, after which they'll drop into their normal
sequential, mutually-exclusive mode. If that's a problem we can use
the spare gate, a resistor, and a capacitor to build a
power-on-reset which will guarantee that the U3's outputs come up
all low whether you press the PAUSE switch or not. Would you like
to do that?

 

[Wayne]

Ok. The only test equipment I have is a digital autoranging
multimeter. I don't know if you saw my other post below, but the 4060
pinout is different than the 4040, and does not have a Q11 output. Q6
is on pin 4, so I changed that. I used Q12 for now instead of Q11.

What I'm seeing now: Pin 9 on U3 (HC175) is cycling from 0V to 5V
every 8 seconds or so. Pin 2 on U3 (HC175) is cycling from 0V to 2.2V
at a large time interval (unsure how long, but greater than 30
seconds), maybe due to me using Q12 on U1 (4060). I have not observed
Pin 7 or 10 on U3 switching states. I'm double checking my wiring
again to make sure I haven't missed something.

Would me using Q12 on U1 cause any problems other than a longer on/off
time?

 

[John Fields]

I'm looking at the data sheet for the 4060, and it's not matching what
you have in the schematic: Q11 doesn't exist on the data sheet (I've
looked at 3), and Q6 is on pin 4, not 6.

---
Yes, I explained that lack of naming consistency between
manufacturers in an earlier post. Regardless of the names used for
the outputs, the pin numbers I called out on the schematic (modified
by the post I made about the error I made) are correct.

Here's the essence of the post:

" In going over the circuit for the last time, (LOL) I found a few
errors:

1. U2-5 should be connected to U1-3, not U1-1

2. C1 should be an 0.18µF polyester cap.

3. R1 should be a standard 2 megohm +/- 5% 1/4W carbon film
resistor."

---

I'm trying to figure out how
the 4060 works, but haven't yet.

---

It's a ripple counter with an on-board oscillator
_ _ _ _ _ _ _ _ _ _ _
CP _| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_
___ ___ ___ ___ ___ _
Q0 ___| |___| |___| |___| |___| |___|
_______ _______ _____
Q1 _______| |_______| |_______|
_______________
Q2________________| |_____________
_____________
Q3________________________________|

and so on...

---

 

[Wayne]

An U1-7 is cycling, don't know if it's 2Hz, but it is cycling.

 

[John Fields]

Ok. The only test equipment I have is a digital autoranging
multimeter. I don't know if you saw my other post below, but the 4060
pinout is different than the 4040, and does not have a Q11 output. Q6
is on pin 4, so I changed that. I used Q12 for now instead of Q11.

What I'm seeing now: Pin 9 on U3 (HC175) is cycling from 0V to 5V
every 8 seconds or so. Pin 2 on U3 (HC175) is cycling from 0V to 2.2V
at a large time interval (unsure how long, but greater than 30
seconds), maybe due to me using Q12 on U1 (4060). I have not observed
Pin 7 or 10 on U3 switching states. I'm double checking my wiring
again to make sure I haven't missed something.

Would me using Q12 on U1 cause any problems other than a longer on/off
time?

---
Since everything on the 4060 is toggling and you're getting clocks
into the 175, the 4060 and all of its circuitry is working.

U3-2 should be cycling between 0V and 5V, so that 2.2V range
indicates that there's probably a wiring error there. I suspect
you've wired U3-2 to U2-1 instead of to U2-2.

As for the timing, I'll wait until I hear from you after you've
read all my other [recent] posts as well as this one, (so we'll be
in sync) and then we'll straighten out the timing, OK?

 

[Wayne]

I couldn't find the datasheet for the 4060 I have: The number on the
chip is SCL4060BE with a picture of a cube with 'S' on each side of the
cube.

 

[John Fields]

I couldn't find the datasheet for the 4060 I have: The number on the
chip is SCL4060BE with a picture of a cube with 'S' on each side of the
cube.

---
OK, here's a link to the data sheet I used:

http://www.semiconductors.philips.com/acrobat_download/datasheets/74HC_HCT4060_CNV_2.pdf

and a link to the final schematic:


If everything works like it should, whenever you power up or hit the
PAUSE switch, U3Q1, Q2, and Q3 should go low and stay low until U1-3
goes low. That should be about 30 minutes with the pot set at
mid-range. During that time, U2-10 should be low, U2-4 should be
high, and the outputs of U10 should be toggling, with U1-7
exhibiting a period of 4 seconds (two seconds high and two seconds
low).

When U1-3 goes high, the reset will be taken off of U3, and 30
seconds later its 3 phase output cycle will begin with U3-2 going
high.

 

[Wayne]

I've made the modifications except for the C2 in the revision C (have
to go get one). I still have not managed to find what I have wrong at
this point. Right now, U3Q1 seems to be staying high (2.2V) and I have
not observed U3Q2 or U3Q3 switching. U1-7 does exhibit a period of 4
seconds as you mentioned, and U1-6 does toggle.

 

[John Fields]

I've made the modifications except for the C2 in the revision C (have
to go get one). I still have not managed to find what I have wrong at
this point. Right now, U3Q1 seems to be staying high (2.2V) and I have
not observed U3Q2 or U3Q3 switching. U1-7 does exhibit a period of 4
seconds as you mentioned, and U1-6 does toggle.

 

[Wayne]

Yes, that happens.

I'm starting to think that U3 is bad, though. I see the clock on pin
9, toggling. Pin 16 (Vcc) has 5V. Pin 1 (clear) is high (5v). Pin 2
(Q1) is 2.2V. Pin 4 (D1) is 5V. Pin 5 (D2) is 2.2V. Pin 7 is 0V,
observed over 60 seconds, never changes. Pin 9 (clock) is toggling
0-5V every 15 seconds or so. Pins 10, 12 and 13 never change from 0V
observed over 60 seconds. I verified that Pin 8 (ground) has 0 ohms to
ground.

On U2, Pin 1 is 5V, Pin 2 is 2.2V, pin 3 is 0v.

If I'm understanding the logic correctly, every time the clock goes low
to high on U3 pin 9, the output should change: Q1 -> Q2 -> Q3.

Any thoughts?

 

[Wayne]

Also, I still can't figure out why I have a difference in voltages.
Shouldn't I have ~5V across the board? Could this be part of the
problem?

 

[John Fields]

Yes, that happens.

I'm starting to think that U3 is bad, though. I see the clock on pin
9, toggling. Pin 16 (Vcc) has 5V. Pin 1 (clear) is high (5v). Pin 2
(Q1) is 2.2V. Pin 4 (D1) is 5V. Pin 5 (D2) is 2.2V. Pin 7 is 0V,
observed over 60 seconds, never changes. Pin 9 (clock) is toggling
0-5V every 15 seconds or so. Pins 10, 12 and 13 never change from 0V
observed over 60 seconds. I verified that Pin 8 (ground) has 0 ohms to
ground.

On U2, Pin 1 is 5V, Pin 2 is 2.2V, pin 3 is 0v.

If I'm understanding the logic correctly, every time the clock goes low
to high on U3 pin 9, the output should change: Q1 -> Q2 -> Q3.

Any thoughts?

 

[Wayne]

MM74C02N is the part number on the chip.

 

[John Fields]

MM74C02N is the part number on the chip.

---
OK.

If U3-1 is high, and U3-9 is toggling, then U3-2 should be either
low (close to 0V) or high (close to +5V), depending on where in the
three phase cycle U3 happens to be.

That 2.2V is the problem, and since it's on U2-2, U3-2 and U3-5,
that indicates that those three points are connected, like they
should be. In my experience, a voltage on a CMOS output about
halfway between Vcc and GND more often than not indicates a high
output shorted to a low output. If that's the case, then the
chip(s) involved in the short should feel warmer than normal, which
is anything other than cool to the touch.

What I'd do is to go over the wiring one more time, making sure I
didn't have an extra wire in there going somewhere it wasn't
supposed to, or a solder bridge creating a short, or maybe even a
burned or cut wire with the exposed conductor touching something it
wasn't supposed to.

If that doesn't help, then I'd disconnect the wire(s) going from
U3-2 to U2-2 and U3-5, connect U2-2 and U3-5 to ground, power up,
and hit the pause switch. U3-2 should wind up low, and if it comes
up high or at 2.2V then U3 is bad.

If it comes up low, then the trouble lies somewhere else and we'll
have to run some more tests to find out where it is.

Post back with what you find and we'll take it from there...

 

[Wayne]

What's the difference between a 74C02 and a 74HC02? My local store
didn't have the 74HC02 in stock, so I got the 74C02.

 

[John Fields]

What's the difference between a 74C02 and a 74HC02? My local store
didn't have the 74HC02 in stock, so I got the 74C02.

---
Here are links to the data sheets:

For the 74HC02,

http://www.fairchildsemi.com/ds/MM/MM74HC02.pdf

and for the 74C02,

http://www.fairchildsemi.com/ds/MM/MM74C02.pdf