MIC1555 Sequential Timer - Triggers on Power Up?

AnalogKid

Joined Aug 1, 2013
9,957
The threshold pin 'takes precedence over the trigger'
Maybe. The 555 was not patented, so many of the today's chip designs are not exact second sources. A while ago there was a thread (or an off-topic bit in a thread) that got into nitty-gritty operational details never clarified on the datasheet, such as which input pin overrides which. SO parts are a real pain to prototype with, but I suggest you verify who overrides whom before committing to fiberglass.

ak

555-Variations-1616949091140.png
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
Maybe. The 555 was not patented, so many of the today's chip designs are not exact second sources. A while ago there was a thread (or an off-topic bit in a thread) that got into nitty-gritty operational details never clarified on the datasheet, such as which input pin overrides which. SO parts are a real pain to prototype with, but I suggest you verify who overrides whom before committing to fiberglass.

ak
This is from the MIC1555 datasheet - and I've confirmed it on the breadboard (well slug tape actually)
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
Here's the current attempt at the 'get it flying with what I have' version, using the MIC1555 and the TLC555CDR I have in stock and incorporating the power on reset RC. I'm not sure what the R4 value should be for this however. The RESET current is super low so I guess it's about the R/C time required?

The LED current slows the R1/C1 charging so I may have to play around with times there too.
 

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eetech00

Joined Jun 8, 2013
3,109
Here's the current attempt at the 'get it flying with what I have' version, using the MIC1555 and the TLC555CDR I have in stock and incorporating the power on reset RC. I'm not sure what the R4 value should be for this however. The RESET current is super low so I guess it's about the R/C time required?

The LED current slows the R1/C1 charging so I may have to play around with times there too.
You can also use two TLC555 timers or a single dual TLC556 timer(14 pin w/two timers). See below.
I've show separate TLC555 timers. Notice there is no glitch on power up.

1635311509663.png
 
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Thread Starter

Slowmatch

Joined Jan 21, 2018
33
Below is the LTspice simulation of AK's basic circuit with a few modifications:

R3 and R5 prevent excess current into the IC inputs from the capacitors if power is suddenly removed.

Edits:
Second Modification below:

Removed added diode D2, and instead moved R2's connection to the drain of the MOSFET to provide the reset function and generate the output pulse width.

The operation is as follows:
At power-up, R2-C2 sets the U1a-U1c latch (red trace) to its reset state (output transistor off).
The input pulse (green trace) flips the state of the U1a-U1c latch.
This starts to pull C1 low through R1 (blue trace)
When C1's voltage reaches the threshold voltage of U1d, its output goes high, turning on the MOSFET (yellow trace).
This low voltage at M1's drain also resets the latch through R2, causing U1a's output voltage to go back high.
This then raises C1's output voltage through D1, causing U1d's output voltage to go back low, turning off the MOSFET.
The value of R2 and C2 determines the time it takes U1a's output to reset high, and thus the output pulse width.

Note that the MOSFET must be a logic-level type MOSFET (max Vgs(th) <2V).


View attachment 251112
I'm just working my way through this version of the CD4093 circuit and have a question: R1 determines the delay, correct? In which case can this be a 1M trimmer to give 0-70 second adjustment? Or does it need a trimmer plus a resistor to set the short end of the delay?

Thanks,
Jon
 

AnalogKid

Joined Aug 1, 2013
9,957
1. Yes. In Wally's simulation, R1 sets the long, turn-on delay. That is the function of R2 + R3 in my circuit.

2. Yes. As in your original circuit, it can be a combination of one fixed and one variable resistor. The fixed resistor sets a lower limit on the range of the delay.

ak
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
1. Yes. In Wally's simulation, R1 sets the long, turn-on delay. That is the function of R2 + R3 in my circuit.

2. Yes. As in your original circuit, it can be a combination of one fixed and one variable resistor. The fixed resistor sets a lower limit on the range of the delay.

ak
Thanks AK.
So in theory R1 could be a single trimmer at zero ohms without causing problems?
Other than the 0 second delay risking burnt fingers(!)
 

AnalogKid

Joined Aug 1, 2013
9,957
So in theory R1 could be a single trimmer at zero ohms without causing problems?
Yes. But. 4000B series CMOS gates have a relatively high output impedance, caused by the channel resistance of the output FETS. IOW, they are seen as "self-protecting" because this resistance limits the available output current. However, they are not rated for even transient operation into a dead short, which is how C2 appears for a few milliseconds at each transition. Technically, there should be a 1K resistor in series with D1, to limit the U1A peak output current into C2. If you delete R3, then the 1K resistor should be between U1A pin 3 and the R2-D1 junction.

I understand your size and weight constraints, but is a single 0805 SMT resistor really a problem?

ak
 
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Thread Starter

Slowmatch

Joined Jan 21, 2018
33
I understand your size and weight constraints, but is a single 0805 SMT resistor really a problem?
I was more just checking my understanding of the circuit to be honest - the extra R will be included because a 0 second trigger would be undesirable: triggering the tail pop up DT just as you start the 8 second motor run on launch. I'll probably set the low end stop at about 10 seconds so that you can fly the model to the top of it's climb and bring it down straight after to check the climbing flight trim.

Thanks for the extra explanation though - the potential for a short was partly why I asked the question.

Again: thanks to everyone for the help so far.
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
I'm getting some Power On weirdness when I combine the DT timer with the Motor timer (https://forum.allaboutcircuits.com/threads/motor-timer-with-brake.182833/)

Now the first stage of the DT Timer is triggering when the battery is connected. Oddly though, if you just disconnect and quickly re-connect it doesn't trigger. It does this only after an hour or so spent disconnected.

The little POR circuit (Q3) I added to hold the second stage MIC1555 high for a moment works when the DT circuit is on its own (without a reset diode across the 1K of Q3) but something else is going on now that it's integrated with the motor timer as shown below.

I'm somewhat baffled!?
 

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AnalogKid

Joined Aug 1, 2013
9,957
You need to add a suppression diode across the motor, and a decoupling capacitor across each IC's power pins. A motor is a big inductor, and actually does not play well with other electronic components.

ak
 

MrSalts

Joined Apr 2, 2020
1,560
Maybe. The 555 was not patented, so many of the today's chip designs are not exact second sources. A while ago there was a thread (or an off-topic bit in a thread) that got into nitty-gritty operational details never clarified on the datasheet, such as which input pin overrides which. SO parts are a real pain to prototype with, but I suggest you verify who overrides whom before committing to fiberglass.

ak
The MIC1555 is not a variant or "second source" of the Signetics NE555 - the pin out from post 1 isn't even close. It is a Microchip 10F series PIC programmed to act kind of like a 555 timer. The OP has been posting the exact part number he's been using for the last 50 posts and everyone knows better because the part number has "555" somewhere so it must be...so here we are.
 

AnalogKid

Joined Aug 1, 2013
9,957
The MIC1555 is not a variant or "second source" of the Signetics NE555 - the pin out from post 1 isn't even close. It is a Microchip 10F series PIC programmed to act kind of like a 555 timer. The OP has been posting the exact part number he's been using for the last 50 posts and everyone knows better because the part number has "555" somewhere so it must be...so here we are.
Actually, everyone does know better.

The MIC in the part number stands for Micrel, not Microchip. I've used this part, and it is not a pre-programmed PIC. For one thing, no PIC that I know of is rated for continuous operation at 18 Vdc.

Here is the datasheet from the link in post #2. Note that MICREL is the very first word.
https://docs.rs-online.com/36de/0900766b8149053d.pdf

And here is the current datasheet from Microchip:
https://www.mouser.com/datasheet/2/...tty_RC_Timer_Oscillator_DS2000573-1890907.pdf

Note that except for the name change, the two datasheets are very nearly identical. Microchip bought Micrel in 2014. They put their name on the datasheet and their logo on the part, but they did not change the part number because they know what a gi-normous headache that is for big-company purchasers.

Also, I was not making a blanket statement about every 555-ish thing on this planet. The history is correct, and the warning is both documented and independent of the pinout. Speaking of that, I can go either way with the non-standard pinout:

a) So what if they rearranged the pins and dropped a function or two. That doesn't mean that the core circuitry is any different from 1972.

b) A different pinout - ??? Oh Lordy, what else did they mess with inside?

Lastly, you claim this part is a microcontroller "programmed to act kind of like a 555 timer", and yet it does not qualify as a "variant"? If that isn't a variant, what is?

ak

ps. You might want to compare the Vdd pinout in slide #7 in your link in post #56, and the Vs pinouts (both of them) on page #2 in his link. Note that one pin is missing; another thing I've never seen is a 5-pin PIC.
 
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AnalogKid

Joined Aug 1, 2013
9,957
To Salts: Now that I've presented my case, I'm very interested in seeing the information you have supporting yours. In past projects I have done what you suggested, using a programmed digital part to mimic other kinds of components. And, a common practice in FPGA and DSP designs is to incorporate the core of a microprocessor within the part. However, I've not seen a commercially available part do this at the jellybean level.

ak
 
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