# 555 Timer delay vs. Delay IC

I need to create a delay in my circuit (about a second) and I'm wondering what are the advantages/disadvantages of using a 555 Timer to create a delay vs using a specialized delay IC like the LTC6994? This is the datasheet for the LTC6994: (http://cds.linear.com/docs/en/datasheet/699412fb.pdf)

• or... use a crystal. – Bradman175 Dec 25 '16 at 0:30

A 555 is about 1/10 the price, but accuracy will likely be less. It also has a plethora of 2nd sources.

The LTC6994 may be lower power, and has most likely higher accuracy.

Of course you could use a microcontroller and do better than either of the above in everything but cost, where the 555 still wins.

• I haven't used a 555 Timer in a long time and I'm actually not sure if it even fits my application. I don't want to delay just a single pulse. When I press a power on/off switch, I want the power to be connected to my circuit after a one second delay, and to remain applied to my circuit. Can a 555 Timer do this? – cheeto Dec 24 '16 at 23:49
• Maybe. It's not really a good way to make a soft power switch if that's what you're thinking, especially for battery power. – Spehro Pefhany Dec 25 '16 at 0:00
• Do you think the LTC6994 is a good option for that application? ...I was looking at 555 timer delay circuits and they're all about delaying pulses. – cheeto Dec 25 '16 at 0:04
• it's probably possible to convince a 555 to do that, but it's probably not the best choice maybe CD4047 – Jasen Dec 25 '16 at 9:30

I doubt that either the 555 or LTC6994 are really great solutions. It may help if you just list the requirements you need to do for your application:

• Sense a button press (are there any further limitations here such as button bounce or if you hold the button down for over 30 seconds?)
• Start a 30 second timer (how accurate? Will you have to adjust it?)
• Set the power on signal (is this an RS flipflop or some other latching logic signal)
• Is there a power off? (button? Timer? Do you press the same button again? Or hold it down for a time period like a PC power button? Or press a second button? etc)

The 555 is certainly cheap but you'll end up paying more for the components around it, especially if you need a potentiometer to adjust the time and a logic chip to hold power on state. Total cost will probably run out to $1.50 if you have an RS latch. The LTC6994 is a great chip but not really designed for such a simple application. You'd probably end up in the$4+ range.

As Sphero so correctly pointed out you may be better considering a 6-8pin MCU like an ATTiny10 SMT (really nice because they do QTouch cap switch sense, and don't require a crystal) for < \$0.90.
Once you have the skills to use the minimal MCU solutions you may hardly ever touch Logic chips again, so it's skills worth having.