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by petermeigs
Wed May 15, 2019 4:16 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Well, I am back at this. I took a bit of time off to wait for the weather to be pleasant enough to install my first water meter. It was not too much trouble. What was not fun was crawling the length of of my home in the crawl space underneath the house. It is about 3 ft or 1 meter high, very dusty a...
by petermeigs
Mon Mar 11, 2019 9:28 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Got it! Thanks. It looks like I just have to move the 100 ohm resistor to between NE555 pin 3 and the first junction before the 10k ohm resistor.
by petermeigs
Mon Mar 11, 2019 7:57 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I (finally) see what you are saying about the zener. I am effectively placing 4.x vdc on ch0 of the adc (MCP3008). The adc (MCP3008) is running on 3.3 v and so I am just reading the max possible 10 bit result. I'm not totally clear on how to correct it. What I'm trying to do is make it so that I pre...
by petermeigs
Sun Mar 10, 2019 10:47 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I've been looking at connection devices via i2c. It looks like if I make the raspberry pi the i2c master I can have it communicate with an arduino with a sketch that runs it at 5v as an i2c slave. Because of the way i2c works, at least in this case, I can connect the rpi to the arduino nano without ...
by petermeigs
Thu Mar 07, 2019 4:57 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Thanks for the comment. I'll use your suggestion for schematics in the future. With regard to the zener: I'll need to study your comments. You are correct that the output voltage of the NE555 running at 5.2v is lower than Vcc. I manually measured it at 4.x with my voltmeter. However, I did test this...
by petermeigs
Mon Mar 04, 2019 6:31 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I got interested in how the NE555 timer would behave if I used it so I put together a test circuit. I twas pretty easy to do because its similar to other tests I have been doing all along. In this one I have two usb ports, one supplying power to the Raspberry pi, and another supplying 5vc to the NE5...
by petermeigs
Thu Feb 28, 2019 8:09 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Thanks for the comments. It is really helpful to have extra eyes looking at my project. I will be using the dc inputs as you suggested. I have drawn it this way in my schematic of Sat Feb 23, 2019 6:41 pm. However, I won't bother with the NE555. I was just getting ready to test how "bouncy" that ite...
by petermeigs
Wed Feb 27, 2019 1:20 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I was able to get some more clarity on the way the water meter ticks work. Every 1 US gallon, the reed switch closes and stays closed for 0.3 gallons. It then opens again for .7 gallons. If water is flowing at the maximum of 34 US gallons per minute. Then the reed switch closes once per 1.74 times p...
by petermeigs
Wed Feb 27, 2019 7:23 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

A 7555 was mentioned before but I had ordered the NE555 before I knew about the 7555 so I thought I just test with the parts I had. I am using a Hunter HC-100-FLOW Meter https://www.hunterindustries.com/irrigation-product/sensors/hc-flow-meter and it has a maximum flow rate of 34 US Gallons per minu...
by petermeigs
Tue Feb 26, 2019 5:27 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Thanks. I was hoping someone with more experienced eyes would offer an opinion and the benefit of that experience here. Having stared at the NE555 in front of the A3700, I recently got the idea that perhaps the A3700 is not even needed at all in the reed switch case. The A3700 was originally there t...
by petermeigs
Sun Feb 24, 2019 5:13 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

It occurs to me that the A3700 in this last circuit perhaps is not needed at all. The NE555 would be operating at 5vdc but we could use a 3.3v zener to drag its voltage down to 3.3v. Then we can connect the OUT pin 3 directly to GPA0 on the MCP23017. We would have to deal with the polarity of the pi...
by petermeigs
Sun Feb 24, 2019 2:41 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Here is my circuit that includes a timer to shut off the reed switch after about .5 secs if we are unlucky and the water meter comes to rest with the reed switch closed. Reed switch with shutoff after .5 secs.png For the time calculation I read https://www.instructables.com/id/555-Timer/#step3 . I b...
by petermeigs
Tue Feb 19, 2019 6:39 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Thanks for the tip. The 7555 is much cheaper too. Of course, I only need two so far and in one case I get 12 for $7.00 USD and in the other I get 30. My wife is starting to notice my parts drawer. I'm not too worried about the 5 vdc current draw for the circuit itself as the power supply can handle ...
by petermeigs
Mon Feb 18, 2019 5:45 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I just found a reference to a 555 timer. Perhaps this will work for me:
http://www.learningaboutelectronics.com ... ircuit.php
by petermeigs
Mon Feb 18, 2019 1:56 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

After mentioning it as a possibility in the last post, I got to worrying about what it would mean if we were unlucky and the water flow stopped such that the reed switch was in a closed position. In an earlier post, I read 3.8 mA through pins 2-3 on the A3700 and measured 4.89 vdc. This would mean a...
by petermeigs
Sun Feb 17, 2019 5:46 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Well, I'm back working on my irrigation sensor. I have reworked my board a bit, removing the connections an d resistors for the last two positions. I only needed 12 and I have room for 16 so I am converting two to use for my reed switch. From our discussion earlier, I've decided to use a separate 5 ...
by petermeigs
Wed Jan 16, 2019 10:38 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

My two port power supply looks similar to the Sweex Brandon92 is showing except mine had US plugs (although it is rated 100-240VAC 50-60Hz) so with a plug adapter it will work anywhere. It has not Ground pin. I guess I am missing the concern here. If either socket goes down, it does not matter to me...
by petermeigs
Tue Jan 01, 2019 6:53 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

A okay, a separate power supply is also a very good idea. You could also use something like this power supply . This will give you also a isolation between the two power rails. Thanks for the tip. It turns out I am using a power supply with two usb sockets https://www.ebay.com/itm/232126014258 anyw...
by petermeigs
Mon Dec 31, 2018 9:38 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

Well, if you are using dc you can use a normal tvs. But if you are using ac you need a bidirectional tvs. And you need to place this across the input of the a3700, close to the connector. So, that if there is a voltage spike (somewhere else) the voltage is limited by this part. And this will protec...
by petermeigs
Mon Dec 31, 2018 5:12 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

... You can add a (bidirectional) TVS diode to protect the input of the A3700. This will clamp the voltage to a certain voltage and protect the input from a over voltage. ... Remember that the reed switch is at the end of a 100ft (30 m) cable. I don't expect to have any other components at that end...
by petermeigs
Tue Dec 25, 2018 5:14 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I have done a test using 100 ft (33 m) of shielded cable. I am using 5vdc from the raspberry pi connecting to a normally-open push button switch (to simulate the reed switch) at the end of the cable. I am connecting to pins 2 and 3 of the A3700 (DC+ and DC-) through a 47 Ohm resistor on each pin. Us...
by petermeigs
Thu Dec 20, 2018 9:52 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

You seem to be doing 2 diff things. 1. check if a reed is closed. 2. check if A37 out changes from high to low. Well, since I have 16 A3700 positions on my circuit but only need 12 of them, I thought I would convert 2 of them to handle the reed switch. Since the A3700 handles hysteresis very well, ...
by petermeigs
Tue Dec 18, 2018 5:11 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I've been reading about reed switches and arcing. I do not know the specifications for the reed switch in the Hunter Flowmeter. I opened it up to look at it and I see that there are two reed switches so I guess one is a spare. They are sealed in epoxy so there is no hope of getting any kind of model...
by petermeigs
Fri Dec 14, 2018 8:57 am
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

It looks like there are lots of choices for LED's. I'll keep these in mind. My next step is to test the reed valve on the Hunter HC100FLOW meter. The cable I will use to connect to an A3700 is 100 feet of AWG 22 3 conductor shielded cable. I get the feeling that 100 feet is not a very long distance ...
by petermeigs
Thu Dec 13, 2018 4:34 pm
Forum: Python
Topic: GPIO.input voltage levels vs edge detection
Replies: 429
Views: 66596

Re: GPIO.input voltage levels vs edge detection

I can't embed Eagle 9.0.1 source for the schematic in the message directly as the character limit is 60,000 characters and the attachment does not support a txt or sch file type

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