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by grahamed
Wed Nov 15, 2017 5:13 pm
Forum: Automation, sensing and robotics
Topic: Raspberry and Arduino RF Communication range problem with rc-switch
Replies: 12
Views: 721

Re: Raspberry and Arduino RF Communication range problem with rc-switch

I use 433MHz a lot. I send the packet maybe 10 times to ensure it gets through at least once. Like the shop-bought remotes and sockets do. My antennae a better than the bitty things within the units. I actually use a PIC micro so timing is not a problem. It's just not terribly good. And that's only ...
by grahamed
Sat Jun 24, 2017 6:34 pm
Forum: Automation, sensing and robotics
Topic: Automatic Car Battery Cut off to prevent rundown andAAA call
Replies: 48
Views: 3866

Re: Automatic Car Battery Cut off to prevent rundown andAAA

Hi So this topic is still running and generating more hot air than most. Having read through it again I see there are any number of factual errors, false assumptions, etc which are then corrected, possibly ignored, forgotten about, resurrected, recycled as firelighters, whatever. For my $2/100 - the...
by grahamed
Sat May 06, 2017 3:28 pm
Forum: Automation, sensing and robotics
Topic: Controlling two 12 v cabinet locks
Replies: 9
Views: 644

Re: Controlling two 12 v cabinet locks

Hi Obviously it should not get hot when turned off, but I don't think this is the best device to connect to a 3V3 sysem. i_o characteristics.jpg (http://www.infineon.com/dgdl/irfp3206pbf.pdf?fileId=5546d462533600a401535628d64a1ff0) Unless used in a very hot place the line does not go much below 4V. ...
by grahamed
Fri Dec 16, 2016 9:59 pm
Forum: Automation, sensing and robotics
Topic: using my doorbell to trigger music that wakes me up
Replies: 3
Views: 891

Re: using my doorbell to trigger music that wakes me up

How is this doorbell receiver powered?
by grahamed
Tue Nov 01, 2016 11:07 am
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi I guess there might be a Windows program that can copy *x partitions but I am not aware of it. For Windows to copy the partition sparsely, i.e. not copy unused space, etc, it would have to understand the structure. I have used an old Partition Magic live CD but it cannot change the write-protecte...
by grahamed
Sun Oct 30, 2016 10:30 pm
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi Adjusting the size of the partition is part of the solution. You then have to copy from old card to new card. Windiskimager copies card not partitions so you end up using dd or such and that means having a spare Linux machine to hand. Actually early versions of Windiskimager did not check sizes r...
by grahamed
Sun Oct 30, 2016 4:33 pm
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi Further findings a USB stick attached during failed SDcard copy was also found to be read-only in the Pi and by Windows, however Windows disk manager recovered it. W10 disk manager says the SDCARD is found, 2 healthy partitions. I can create a new file on the (still read-only) SDCARD boot partiti...
by grahamed
Thu Oct 27, 2016 1:54 pm
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi drgeoff

I know it's not, that's why I'd really like Raspian to allow expansion to nominal size less 10%. I don't think that will happen either. At this time I do not trust SCARD copier in accessories. I don't like what it does either, copy a live file system... never did that in my day.
by grahamed
Thu Oct 27, 2016 11:38 am
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi hippy I think you are correct. I also think it was SDCARD copier what done it. I have no evidence for this excepting that I saw it immediately after a failed attempt to copy a card. But how to undo it? Googling gets many hits re the w/p switch found on full size cards, and many references to Wind...
by grahamed
Thu Oct 27, 2016 11:02 am
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi Thanks I never buy such things from eBay - I know people who do and are surprised when their incredibly well-priced card/stick turns out to fill up quicker than its alleged capicity would suggest. Unless two cards are the same size one will be bigger than the other.....irrespective of other quali...
by grahamed
Thu Oct 27, 2016 10:27 am
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi again

SDformatter says the card is write-protected.

So I shall buy some more 16G cards.....and hope the new 16G is as big as the old 16G, or has that problem been sorted? - but please do not say use SDCARD copier.
by grahamed
Thu Oct 27, 2016 10:03 am
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Re: Strange things after SDCARD backup

Hi OK, thanks for the reply. I was hoping that Linux had somehow become read-only and could be reset. Unless it's an amazing co-incidence it happened during SDCARD COPIER which is a bit worrying, I will use Win32DiskImager to copy off this card, format it with SDformatter, write the earlier backup b...
by grahamed
Wed Oct 26, 2016 10:12 pm
Forum: Troubleshooting
Topic: Strange things after SDCARD backup
Replies: 17
Views: 1401

Strange things after SDCARD backup

Hi I am quite sure that i have got hold of the wrong end of the stick here; otherwise something rather odd is happening. Well I think it's odd, maybe it is well-known. If I edit a file (such as /etc/rc.local as root), save it, reopen it, see it has changed, reboot, reopen it find it has changed back...
by grahamed
Sat Apr 23, 2016 2:17 pm
Forum: Automation, sensing and robotics
Topic: Monitoring electrical device activation times
Replies: 4
Views: 568

Re: Monitoring electrical device activation times

Hi The sensor is a current transformer (CT). The CT produces a secondary (output) current proportional to the primary current according to the turns ratio. In this case 1:2000 so 30A will give 15mA in the secondary. The user must choose a suitable resistor to convert this current into a voltage. 1k ...
by grahamed
Fri Apr 22, 2016 9:27 pm
Forum: Automation, sensing and robotics
Topic: PCF8591P and 50-70mV difference
Replies: 3
Views: 425

Re: PCF8591P and 50-70mV difference

Hi

Where are you connecting the meter? Is it across the battery terminals or across the input of the ADC?
by grahamed
Fri Apr 15, 2016 10:57 pm
Forum: Automation, sensing and robotics
Topic: Two wire temperature sensor
Replies: 3
Views: 745

Re: Two wire temperature sensor

Hi

Looks like a K-type thermocouple. If it is then MAX6675 looks like a good solution. The plug is often a clue.
by grahamed
Sun Mar 27, 2016 12:07 pm
Forum: Automation, sensing and robotics
Topic: Need help using illuminated toggle switch!
Replies: 3
Views: 595

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: 595

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: 711

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: 1954

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: 3169

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: 1673

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: 2085

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: 2085

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: 12340

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 ...

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