Help Debug Circuit

[ThomsCircuit]

If you have a couple of 555's laying around

I do like using the 555's It took a while but i did make the schematic in Design Spark. I haven't put in the resistor and cap values but I did add the linkage for the Peak Detector you helped me with and a small digital volt meter. The reading comes from the DC side of the Zener Diode of the Peak Detector. Its configured in a way that the meter is only on while the circuit is closed.

 

[eTech]

I do like using the 555's It took a while but i did make the schematic in Design Spark. I haven't put in the resistor and cap values but I did add the linkage for the Peak Detector you helped me with and a small digital volt meter. The reading comes from the DC side of the Zener Diode of the Peak Detector. Its configured in a way that the meter is only on while the circuit is closed.

1. There is an error on your schematic.
U1 pin-4 and R10 are connected wrongly. Please review the schematic in post #53.

2. What is the part number for the SSR? I'd like to look up the datasheet. You may be able to drive the SSR directly with the 555 and eliminate a relay.

 

[ThomsCircuit]

1. There is an error on your schematic.
U1 pin-4 and R10 are connected wrongly. Please review the schematic in post #53.

2. What is the part number for the SSR? I'd like to look up the datasheet. You may be able to drive the SSR directly with the 555 and eliminate a relay.

Got it. thank you.
The SSR is a generic made under a few labels. spec sheet attached. I have the 40Amp

 

[eTech]

Got it. thank you.
The SSR is a generic made under a few labels. here is a spec sheet for the 40Amp. Wait that is the wrong one. hold on

um....don't use that one if your switching an AC load. That is a DC SSR.

 

[ThomsCircuit]

That is a DC SSR.

yes. i noticed. i have the AC type 40Amp. Sorry for the mixup

 

[eTech]

yes. i noticed. i have the AC type 40Amp. Sorry for the mixup

Is it a DC input to AC output type SSR?

 

[ThomsCircuit]

Is it a DC input to AC output type SSR?

YES.

SSR-40 DA 40A DC 3-32V to AC 24-380V SSR Single Phase Solid State Relay​

 

[ThomsCircuit]

In this circuit I use four of the sections as open-collector inverters

Would it be good practice to ground all unused pins?

 

[ThomsCircuit]

Updated AK's design. Added component values, grounded unused pins. Still need Var resistor values.

 

[ThomsCircuit]

Made correction to ETech's design, added values.

 

[AnalogKid]

Would it be good practice to ground all unused pins?

In this ***particular*** case - no.

1. The 2004's unused have internal resistors to GND. This puts the outputs in known and safe states.

2. It is rarely a good idea to ground unused outputs, because there is a good chance that their unused state might not be GND internally, creating a conflict that could kill the chip. In the case of 2004's, this does not apply, but in something with a totem-pole output (as opposed to open-collector) this is a definite problem.

ak

 

[ThomsCircuit]

The 2004's unused have internal resistors to GND.

Thank you. Ill update it. How about inserting a variable pot so i can adjust the delays

 

[AnalogKid]

based on the info you provided i think R1 for the ON delay and R2 would be for the OFF delay.

Correct.

I have tried to understand the formula to determine what combination is needed I have to confess my algebra is very poor. My kids however are extremely smart. I mean it too. My oldest is a scientist and my youngest is the youngest person in her Algebra II Honors class.

Something for your kids to chew on ...

Here is a medium-level explanation of the math. Note that this is a general description, and rarely applies directly to any particular circuit without adjustments. The good news is that one time constant is around 90-95% correct for the ULN2004 circuit (based on what I'm sure is a reasonable approximation). I'll try to write that up later.

RC circuit - Wikipedia

en.wikipedia.org

https://en.wikipedia.org/wiki/RC_time_constant (only the opening section)

Because the input to a ULN2004 section has resistors (and diodes) to GND, the external timing resistor is not the only resistance that affects the timer period. The external resistance combines with the internal resistance to form an equivalent resistance, called the Thevenin equivalent. In this case the math is the same as two resistors in parallel.

Thévenin's theorem - Wikipedia

en.wikipedia.org

No, I'm not showing off, or trying to scare anyone. This really is the cooked-down math for this circuit. If you want to be scared ...

Laplace transform - Wikipedia

en.wikipedia.org

ak

 

[ThomsCircuit]

Something for your kids to chew on ... (only the opening section)

i passed this on to my daughter. i told her i wanted to know what resistor i would need to produce a 1 second delay. i gave her the cap value of 470uf and the 12 voltage source. she said there are too many missing pieces of information to find the value.
The problem is i do not understand what im reading. i assume i am trying to find the resistor value using this formula

 

[ThomsCircuit]

Because the input to a ULN2004 section has resistors (and diodes) to GND, the external timing resistor is not the only resistance that affects the timer period.

i understand this to mean i need only to replace R1 with a Var Resistor. What that resistor value range is I don't know.

 

[ThomsCircuit]

The good news is that one time constant is around 90-95% correct for the ULN2004 circuit

I believe the formula is as follows as in your ULN2004 IC
(r1 + r2) x C1 = seconds
r1= Resistor on your schematic
r2 = Resistor inside the ULN
C1 = capacitor in your schematic

(10+2.7) x .470 = 6 seconds
so to give this a range of 6 - 10 seconds I would add a 9K Variable Resistor in series

 

[ThomsCircuit]

I applied the same formula to E-Tech's schematic and came up with
82 x .010 = .82
then added the var and got 5.82
so the range is .82 - 5.82 seconds turn on delay

so i dont know if im ready for this but does it matter the cap / resistor combo values? or as long as it meets the requirements its fine to use what ever cap/res combination you like.

 

[ThomsCircuit]

Is it a DC input to AC

SSR AC/DC SPEC

 

[AnalogKid]

The internal resistances in a ULN2004 stage add up to 20.9 K. For the Thevenin equivalent impedance of a voltage divider, this is in parallel with the external 10 K resistor, for a value of 6764 ohms. With a 470 uF capacitor, one time constant equals 3.81 seconds.

Why one time constant? The voltage on a capacitor charging up from 0 V to some source voltage Vs through a resistance equals 63.2% of Vs after one time constant. With a 10 V source, a 1 M resistor, and a 1 uF capacitor, the time constant is 1 second, and the capacitor voltage will be 6.32 volts after 1 second. The input transition voltage of a 2004 is approx. 5 V. In a 12 V circuit, this is 62.5% of Vs, which is very close to the 1 time constant value. This is the assumption I would use to find starting point values for the timing components.

That 5 V transition level sets a minimum value for the external resistor. At 20 K the input voltage never will go high enough to cause the stage to change state, and that 5 V transition voltage is not tightly defined. If you want a 2:1 adjustment range, then let 10K be the maximum value for the external resistance, calculate the capacitor value needed for the max desired time delay, and then use that capacitor value to calculate the resistance value for the minimum desired time delay.

ak

 

[ThomsCircuit]

The internal resistances in a ULN2004 stage add up to 20.9 K.

In a search I saw a few values. I did not know which one was the internal R. So its 20.9k
When I do (10k + 20.9k) x .470 I get 14.5
How do you get 3.81?