looking for a 555 timer circuit

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

Reply to
Wayne
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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.

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John Fields
Professional Circuit Designer
Reply to
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.

Reply to
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?

Reply to
Wayne

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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
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Reply to
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?

Reply to
Wayne

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Yes, I explained that lack of naming consistency between
manufacturers in an earlier post.  Regardless of the names used for
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Reply to
John Fields

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

Reply to
Wayne

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

Reply to
Wayne

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

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

Reply to
Wayne

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If U3-1 goes low when you hit the PAUSE switch, U3-2, 7, and 10
should all go low (close to 0V).  Does that happen?
Reply to
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?

Reply to
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?

Reply to
Wayne

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Is U2 an HC02?
Reply to
John Fields

MM74C02N is the part number on the chip.

Reply to
Wayne

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OK.

If U3-1 is high, and U3-9 is toggling, then U3-2 should be either
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Reply to
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.

Reply to
Wayne

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Here are links to the data sheets:

For the 74HC02,
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Reply to
John Fields

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