Signal Delay Circuit - Page 1
Forum section: electronics / projects

author: Radardude
author_rank: Newbie
timestamp: January 17, 2014, 02:03:05 pm
content: I have a tankless water heater and a water solar system. I'm designing a circuit to delay the tankless heater from turning on allowing the hot water to reach the tankless heater. A signal from the internal flow sensor activates the tankless heater. IC1 is a retriggerable monostable multivibrator. The IC1 output pulse is longer the than slowest signal freg. R2 and C2 will provide the delay of the signal through IC2. My question, is there a simpler way to do this or a better way?

author: tszaboo
author_rank: Super Contributor
timestamp: January 17, 2014, 06:23:39 pm
content: Quote from: Radardude on January 17, 2014, 02:03:05 pmIf you are going to fool yourself that putting an RC on a digital signal is a good solution, at least put a schmitt trigger input part after it.

author: dannyf
author_rank: Super Contributor
timestamp: January 17, 2014, 06:31:21 pm
content: Quote1. 555 timer, or2. mcu.

author: Radardude
author_rank: Newbie
timestamp: January 17, 2014, 09:52:15 pm
content: Quote from: NANDBlog on January 17, 2014, 06:23:39 pmPin 1 of IC2 is like a switch, it will slowly charge up (about 60 secs) until it is seen as a high allowing the signal on pin 2 to pass out of pin 4. Pin 1 will remain high as long as the water is flowing. So I don't think I need a schmitt trigger. Timing of the signal is not important. I'm trying to keep the component count as low as possibly.

author: electronics man
author_rank: Frequent Contributor
timestamp: January 17, 2014, 10:27:18 pm
content: I think an mcu is the best idea as you can easily experiment whith different times. You could use a 555 time but it is more difficult to experiment whith diferent times mcu is just the easiest. All you need is a cheep small mcu like picaxe 08 if you don't have another one in your BOM or you could use any mcu you want.

author: Radardude
author_rank: Newbie
timestamp: January 19, 2014, 06:17:43 am
content: Quote from: electronics man on January 17, 2014, 10:27:18 pmAt first when you suggested to use a MCU I thought that was such an overkill. I have used Basic Stamps and Basicx BX24p on several elaborate projects in the past. But I didn't realize that such small and inexpensive MCU existed. I will use this MCU because of the small packaging and the small learning curve involved. It will provide a smaller component count than my design. This information opens up another wave of projects for me. Thanks for sharing.

author: Skimask
author_rank: Super Contributor
timestamp: January 19, 2014, 06:32:06 am
content: PIC10F200

author: calexanian
author_rank: Super Contributor
timestamp: January 19, 2014, 07:39:18 am
content: How about just a standard time delay relay. Nice, cheap, ready to go, and reliable. Amazon has many upon manys of them.

author: Radardude
author_rank: Newbie
timestamp: January 19, 2014, 09:02:26 am
content: Quote from: calexanian on January 19, 2014, 07:39:18 amI don't have the space for a time delay relay. It would still require additional components because the flow sensor signal (1hz to 100hz 0 to 5V) which is the activating signal.