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by grahamed
Sun Mar 27, 2016 12:07 pm
Forum: Automation, sensing and robotics
Topic: Need help using illuminated toggle switch!
Replies: 3
Views: 1282

Re: Need help using illuminated toggle switch!

Hi again Try wiring a few-k resistor between 3V3 and the GPIO pin (to gently pull the pin high) and connect a wire to 0V and dab it on the pin (to drag it low). Your program then has a chance. If you don't have a resistor use one of the GPIOs which has a resistor built-in. When you know your program...
by grahamed
Sun Mar 27, 2016 11:15 am
Forum: Automation, sensing and robotics
Topic: Need help using illuminated toggle switch!
Replies: 3
Views: 1282

Re: Need help using illuminated toggle switch!

Hi As this is specified as a 12V device - presumably for use in a car - I assume that the LED has a in-built resistor sized for 12V operation. The page makes no mention of needing an additional resistor. So maybe the LED is on but is v. dim. Try connecting it to a handy 12V source - like a car, if y...
by grahamed
Sun Mar 27, 2016 11:07 am
Forum: Automation, sensing and robotics
Topic: False positive press of a button
Replies: 6
Views: 1205

Re: False positive press of a button

Hi The switch wiring looks OK to me. The LHS contact is pulled to ground by 220R and the switch makes it high when pressed I think. i think maybe liudr is confused by the use of black both for 0V and for the switch wire. The LED wiring on the other hand - no resistors can I see - try adding some may...
by grahamed
Sat Mar 26, 2016 12:01 am
Forum: Automation, sensing and robotics
Topic: getting two Pis to dump sensor readings into one SQL file
Replies: 31
Views: 3637

Re: getting two Pis to dump sensor readings into one SQL fil

Hi Having recently 'upgraded' my house monitor/ control system to use mainly ESP8266 I now see the synchronisation problem. Previously I got my results mainly from Pi's they were usually more or less on time and a bit of Python fudging in whichever sensor Pi got the scheduled time into the SQL. Now ...
by grahamed
Thu Mar 24, 2016 7:24 pm
Forum: Beginners
Topic: Detecting Electric Current
Replies: 34
Views: 6443

Re: Detecting Electric Current

Hi just a couple of quick points - I often find that a scope produces a lot of information much of which is, in fact, irrelevant. Wood and trees spring to mind. the output of a current transformer must be a (rough) sinusoid at 50/60V, generally meters are quite good at reading this. as to direction ...
by grahamed
Thu Mar 24, 2016 7:09 pm
Forum: Automation, sensing and robotics
Topic: Reading temperature from Oregon sensors?
Replies: 13
Views: 4322

Re: Reading temperature from Oregon sensors?

Hi Joan your stuff looks amazing - my admiration knows no bounds. It is clear that your software can display/count/decode most things but can one use it in the middle of a house automation system, bearing in mind that the sensors are asynchronous and (I assume but maybe, hopefully I am wrong) the CP...
by grahamed
Thu Mar 24, 2016 6:47 pm
Forum: Automation, sensing and robotics
Topic: RPi 2 4-20mA sensor
Replies: 9
Views: 4030

Re: RPi 2 4-20mA sensor

Hi Mikronauts

The comment about the worst thing was meant for the OP ..... s/he needs to consider what happens when the Pi thinks the pressure vessel is not even close to boiling, but really...it is. Or whatever.

Paranoia rules, imagination of how bad things can go is also useful.
by grahamed
Thu Mar 24, 2016 11:54 am
Forum: Automation, sensing and robotics
Topic: RPi 2 4-20mA sensor
Replies: 9
Views: 4030

Re: RPi 2 4-20mA sensor

Hi Mikronauts Yes it does completely depend on the measurement system being floating (though I could probably cope with a grounded system provided I had full knowledge of the ground arrangements). In this case it seems that these floating (at least the dox don't say otherwise, and it must be checked...
by grahamed
Wed Mar 23, 2016 10:41 pm
Forum: Automation, sensing and robotics
Topic: Using rain sensor?
Replies: 12
Views: 20786

Re: Using rain sensor?

Hi I have had many of these modules. They all said they had analog output but really they didn't. The 8-leg thing is a comparator which basically compares the resistance of the sensor with a fixed resistor (by reading the voltage of the divider formed by the sensor and the high value resistor). The ...
by grahamed
Wed Mar 23, 2016 10:30 pm
Forum: Automation, sensing and robotics
Topic: Reading temperature from Oregon sensors?
Replies: 13
Views: 4322

Re: Reading temperature from Oregon sensors?

Hi

Oregon Scientific protocols are well documented - ask Google. Years ago I had it working but then the OS sender died. I used a PIC. A Pi is not ideal for decoding these signals.
by grahamed
Wed Mar 23, 2016 10:23 pm
Forum: Automation, sensing and robotics
Topic: RPi 2 4-20mA sensor
Replies: 9
Views: 4030

Re: RPi 2 4-20mA sensor

Hi It is a long time since I used 4-20mA and reading the datasheet is no substitute for having a deice to test........ The datasheet connection diagram 907021/21-2-34-005 shows +11-35V going to the sensor with the -ve current being the data. The sensor is fully floating with no electrical connection...
by grahamed
Wed Mar 09, 2016 10:04 pm
Forum: Automation, sensing and robotics
Topic: Using Pi as PID with thermocouple, need verification
Replies: 9
Views: 1558

Re: Using Pi as PID with thermocouple, need verification

Hi You must consider the switch to be two devices - the switch itself and the LED. These are, and must be, completely separate. The LED is specified as 12V - you could try it on 5V - it might be OK, it might be too dim, it might not come on at all but will not be damaged. The LED must be connected t...
by grahamed
Wed Mar 09, 2016 8:34 pm
Forum: Automation, sensing and robotics
Topic: Best SSR kit
Replies: 14
Views: 3620

Re: Best SSR kit

Hi Agreed, use a a pair of optos. Connect the transistors across the switches - 4 wires - no other connection to the foreign device. You don't need to worry about which way to connect - one way will work, the other won't, so you are 50/50. If one or both don't work just swap that connection. 4N25, 4...
by grahamed
Wed Mar 09, 2016 2:56 pm
Forum: Automation, sensing and robotics
Topic: Best SSR kit
Replies: 14
Views: 3620

Re: Best SSR kit

Hi

What do mean by a low-current device?

If you mean it's a d.c load then an SSR would be inappropriate (as 99% of them expect an a.c. load) . You would need a simple BJT or FET, or a BJT/FET plus relay, or if the current and voltage are low enough just a resistor.
by grahamed
Tue Mar 08, 2016 11:09 pm
Forum: Automation, sensing and robotics
Topic: Using Pi as PID with thermocouple, need verification
Replies: 9
Views: 1558

Re: Using Pi as PID with thermocouple, need verification

Hi again The switch is said to have n/o and n/c contacts - i.e. 3 terminals aka. single pole changeover, aka single pole double throw or SPDT (I don't know how the illumination is arranged). You must not connect these three terminals as you show them on your diagram. Have a look for a single pole si...
by grahamed
Mon Mar 07, 2016 11:32 pm
Forum: Automation, sensing and robotics
Topic: Using Pi as PID with thermocouple, need verification
Replies: 9
Views: 1558

Re: Using Pi as PID with thermocouple, need verification

Hi
The wiring to the switch looks strange. Normally I'd expect to see either 2 wires - single pole switching - or 4 wires - double pole switching (better). Unless this an illuminated switch?
by grahamed
Sat Feb 13, 2016 4:44 pm
Forum: Automation, sensing and robotics
Topic: How do I find the expected load current of an electric motor
Replies: 31
Views: 4135

Re: How do I find the expected load current of an electric m

Hi GT2RFan - you have been amazingly patient with him - perhaps you would now like to spend the same time explaining to him what an H-bridge is, why he needs one, and how he is groping his way towards inventing one. Perhaps not. baranobeefdip - once you understand what a H-bridge is you will underst...
by grahamed
Sat Feb 13, 2016 10:36 am
Forum: Automation, sensing and robotics
Topic: How do I find the expected load current of an electric motor
Replies: 31
Views: 4135

Re: How do I find the expected load current of an electric m

Bidirectional control? If you had mentioned this before I guess a dozen good folks would have said to look for an "Hp-bridge".
by grahamed
Thu Feb 11, 2016 7:46 pm
Forum: Automation, sensing and robotics
Topic: getting two Pis to dump sensor readings into one SQL file
Replies: 31
Views: 3637

Re: getting two Pis to dump sensor readings into one SQL fil

"Why use 2 Pi's....."

Perhaps for the same reason as I use 4 - physical location and wiring.
by grahamed
Tue Feb 09, 2016 11:14 pm
Forum: Automation, sensing and robotics
Topic: A few questions about my 433MHz automation plan
Replies: 8
Views: 3544

Re: A few questions about my 433MHz automation plan

1) Yes, though I cannot say whether your receiver will work on 3V3 - mine do. 2) The receiver ramps up its sensitivity when there is no signal until it starts to pick any old noise. When a signal comes it is much bigger than the noise so the output becomes clean. The gain remains low for quite a few...
by grahamed
Tue Feb 09, 2016 9:33 pm
Forum: Automation, sensing and robotics
Topic: Current Sensing
Replies: 21
Views: 4902

Re: Current Sensing

Does the 310 come and go as the lamp is turned on and off?

How do know that you should b getting 512?
by grahamed
Tue Feb 09, 2016 9:14 pm
Forum: Automation, sensing and robotics
Topic: A few questions about my 433MHz automation plan
Replies: 8
Views: 3544

Re: A few questions about my 433MHz automation plan

1) Never connect a 5V device to a GPIO directly. Either power the device from 3V3 and accept reduced performance maybe - how much range do you need? - or use a level shifter. 2) The tutorial correctly shows what the input looks like. 3) I use a PIC running at 5V, 3V3 reduces range somewhat and, stra...
by grahamed
Sat Dec 26, 2015 7:31 pm
Forum: Automation, sensing and robotics
Topic: Hall-voltmeter Pi
Replies: 3
Views: 1065

Re: Hall-voltmeter Pi

Well said Burngate.

I agree with the need for amplification - the OP should have a look at an "instrumentation amplifier" particularly the low drift and CMRR.
by grahamed
Fri Dec 18, 2015 8:33 pm
Forum: Automation, sensing and robotics
Topic: Circuit pictures- or circuit diagrams?
Replies: 10
Views: 3228

Re: Circuit pictures- or circuit diagrams?

When I said jpg I meant png. In fact anything but jpg it seems.
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tmp.png (2.69 KiB) Viewed 2803 times

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