MIC1555 Sequential Timer - Triggers on Power Up?

eetech00

Joined Jun 8, 2013
3,111
Below is the LTspice simulation of AK's basic circuit with a few modifications:

I added D2 to reset the circuit after the time-out.

I eliminated C3 and R4, and replaced them with R4 in series with D1 to provide about a half second delay in the reset at the output to give the half second output pulse.
Thus C1 does double-duty.

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

View attachment 251098
What does D2 do?
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
I've just come across the CSS555C: http://www.customsiliconsolutions.com/downloads/Revised Standard products/CSS555 Application Circuits.pdf

Page 10 has a "One Shot with Delayed Pulse" circuit with delays set by a couple of resistors.

Excitingly, it seems to do exactly what I want in a small single package (The SOIC8 version is CSS555-IS) but - disappointingly, it seems difficult to source (I'm in the UK) except for possibly Jameco who are on the wrong side of the pond:
https://www.jameco.com/z/CSS555-IS-...s-CSS555-Micropower-Timer-SOIC-8_2146425.html
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
Okay.
But the modified circuit has the same number of parts as the original.
Thanks for the help crutschow.

The circuit reset is definitely important for me. The ideal scenario is to be able to turn up to the field, connect the battery, push the button and fly - knowing that the DT will terminate the flight. Having to reset after every flight/retrieval adds a step that I know at some point would be forgotten - resulting in the model flying away.
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
I've spent some time drawing up the MIC1555/TLC555CDR combo circuit. It also gives me the option of having an LED light while the first stage runs. I think this is probably the quickest route to a real world flying timer at the moment. Before I make it I will spend some time on AKs circuit and see if it saves me space/weight...

I've also been looking at the PIC10F200 option and watching some tutorials. This would be the long game option and I'm definitely seduced by the small footprint this provides but I have a lot of questions...

Alternatively the CSS555S would be worth me paying international shipping if I have read the data sheet correctly and it does what I think it does...
 

crutschow

Joined Mar 14, 2008
29,524
I've just come across the CSS555C: http://www.customsiliconsolutions.com/downloads/Revised Standard products/CSS555 Application Circuits.pdf

Page 10 has a "One Shot with Delayed Pulse" circuit with delays set by a couple of resistors.
But did you notice this in the data sheet?
Configuration data for the counter is held in EEPROM. A straightforward four-wire interface provides Read/Write access to the memory.
So it appears you will need a SPI digital connection to program it.
 

crutschow

Joined Mar 14, 2008
29,524
I've spent some time drawing up the MIC1555/TLC555CDR combo circuit. It also gives me the option of having an LED light while the first stage runs.
Did you solve the startup problem with that circuit?

Below is the CD4093 circuit with an added LED (D2) that lights when the circuit is timing.
The CD4093 can only provide about 1mA to the LED but that should be enough to make a high-brightness type LED readily visible.

1635264007437.png
 
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AnalogKid

Joined Aug 1, 2013
9,974
it appears you will need a SPI digital connection to program it.
The company sells a USB-to-SPI dongle with a software GUI that *appears* to make it pretty simple to program.

Interesting part. Exar used to make a timer parts that were a 555 core with an onboard divider. Great parts, long gone.

ak
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
So you are willing to change your entire design, but not willing to change a single chip because of the footprint.
Sorry, you've lost me here. Which chip should I be willing to change? I'm genuinely not aware of what you are referring to.

As I said I'm interested in any solution that helps me keep the weight/size down but I do have to consider certain practicalities. I already have on my desk a few of the MIC1555MY-TR that I originally linked to (the SOT-23), as well as the TLC555CDR (which is SOIC8) so it seems sensible to prototype with these using the RESET pin held low on start up.

If I can get the size down significantly with the 4093 circuit then I may pursue that ie go buy some!

In the long run I can see the appeal of a Microcontroller but for me that means learning coding from scratch and significant outlay for a programmer etc. probably worth it but quite an investment and and a somewhat overwhelming prospect.
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
But did you notice this in the data sheet?
Configuration data for the counter is held in EEPROM. A straightforward four-wire interface provides Read/Write access to the memory.
So it appears you will need a SPI digital connection to program it.
Hmm thanks, I had missed that. I'll go back and have a better look...
 

eetech00

Joined Jun 8, 2013
3,111
Sorry, you've lost me here. Which chip should I be willing to change? I'm genuinely not aware of what you are referring to.

As I said I'm interested in any solution that helps me keep the weight/size down but I do have to consider certain practicalities. I already have on my desk a few of the MIC1555MY-TR that I originally linked to (the SOT-23), as well as the TLC555CDR (which is SOIC8) so it seems sensible to prototype with these using the RESET pin held low on start up.

If I can get the size down significantly with the 4093 circuit then I may pursue that ie go buy some!

In the long run I can see the appeal of a Microcontroller but for me that means learning coding from scratch and significant outlay for a programmer etc. probably worth it but quite an investment and and a somewhat overwhelming prospect.
The MIC1555 needs a CS pin like the MIC1557. The documentation is poor.
The document shows a 1555 monostable circuit with a CS pin, but the footprint shows no CS pin. So…if that is meant to be a 1557, then that should work for you.
Use the CS pin as a POR to hold the chip output disabled during startup. It would only require a cap and resistor (and maybe a diode) to implement.
 

Thread Starter

Slowmatch

Joined Jan 21, 2018
33
The MIC1555 needs a CS pin like the MIC1557. The documentation is poor.
The document shows a 1555 monostable circuit with a CS pin, but the footprint shows no CS pin. So…if that is meant to be a 1557, then that should work for you.
Use the CS pin as a POR to hold the chip output disabled during startup. It would only require a cap and resistor (and maybe a diode) to implement.
If I understand it correctly:

The MIC1555 comes in two packages:
SOT-23 with no CS pin (ie a compromise to get the 555 into a 5 pin package)
UTDFN with CS pin

The MIC1557 is really a different chip.

Unfortunately (from the perspective of the POR) I have the SOT-23 but the UTDFN is probably beyond my soldering ability anyway.

The threshold pin 'takes precedence over the trigger' so I guess that's the reset option - holding it high briefly during power up does keep the second stage from triggering. I did think of using a P FET with R/C to do this but in bumping up the parts count it probably negates the benefit of the SOT-23 - hence the reason for using the SOIC 8 555 for the second stage instead.
 

eetech00

Joined Jun 8, 2013
3,111
If I understand it correctly:

The MIC1555 comes in two packages:
SOT-23 with no CS pin (ie a compromise to get the 555 into a 5 pin package)
UTDFN with CS pin

The MIC1557 is really a different chip.

Unfortunately (from the perspective of the POR) I have the SOT-23 but the UTDFN is probably beyond my soldering ability anyway.

The threshold pin 'takes precedence over the trigger' so I guess that's the reset option - holding it high briefly during power up does keep the second stage from triggering. I did think of using a P FET with R/C to do this but in bumping up the parts count it probably negates the benefit of the SOT-23 - hence the reason for using the SOIC 8 555 for the second stage instead.
the CS pin needs to be held low at startup to keep the output disabled.
Dont need a PFet for that, just a cap and resistor.
 

crutschow

Joined Mar 14, 2008
29,524
The CD4093 comes in a small outline surface-mount package with pins on 0.025" centers.
The circuit requires just one of these packages.
Is that small enough for your purposes?
 
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