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by davidcoton
Fri Oct 20, 2017 9:56 pm
Forum: Troubleshooting
Topic: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT
Replies: 12
Views: 295

Re: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT

Vincintosh wrote:
Fri Oct 20, 2017 9:22 pm
Alright, thank you I ordered it. How can I tell wheter or not I need that extra resistor and where should it go?
Try it. If it doesn't work (experience with similar boards suggests it will) ask again.
by davidcoton
Fri Oct 20, 2017 9:14 pm
Forum: Beginners
Topic: Need help with "updating" and what command does what.
Replies: 9
Views: 163

Re: Need help with "updating" and what command does what.

apt update -- updates the catalogues of available software to determiine what needs upgrading apt upgrade -- downloads and installs software that update marked for upgrade apt dist-upgrade -- as upgrade, but does a more thorough job of checking and updating dependencies. rpi-update -- Installs the ...
by davidcoton
Fri Oct 20, 2017 8:48 pm
Forum: Troubleshooting
Topic: Am I asking too much of a Pi Zero W?
Replies: 3
Views: 113

Re: Am I asking too much of a Pi Zero W?

Does it work with just one program at a time? If not, fix the program that fails. A Pi3B won't help. If it does, then you might be in weird interaction territory. A Pi3B may or may not help. Keep an eye on memory use via "top" in a console window. First guess would be a memory leak in one of the pro...
by davidcoton
Fri Oct 20, 2017 8:43 pm
Forum: Troubleshooting
Topic: No PWR led, ACT led very dim and gets hot! (A+)
Replies: 40
Views: 1106

Re: No PWR led, ACT led very dim and gets hot! (A+)

davidcoton wrote: Edit: Ugh, the post from drgeoff that I mentioned has gone....
... and returned in a shiny new revised edition :D :lol:
by davidcoton
Fri Oct 20, 2017 8:40 pm
Forum: Troubleshooting
Topic: induction problem gpio relay load
Replies: 34
Views: 2012

Re: induction problem gpio relay load

Thanks, drgeoff. With that calculation my original capacitor recommendation for DC will also work for AC. The same could also be used across the solenoid coil. The voltage rating is even more important with AC than DC, since the AC peak is 1.4 times the normally quoted RMS value. Note that protectio...
by davidcoton
Fri Oct 20, 2017 8:32 pm
Forum: Troubleshooting
Topic: i2c with MCP23016 - can´t see connected
Replies: 7
Views: 156

Re: i2c with MCP23016 - can´t see connected

According to the data sheet it will run at 3V3. Although the I2C bus is powered by 3V3 pull-ups on the Pi and is therefore independent of the expander supply voltage, it will still be safer to power the chip at 3V3, unless you need 5V outputs. You may also need ground connections to pins 1 and 8 as ...
by davidcoton
Fri Oct 20, 2017 8:23 pm
Forum: Troubleshooting
Topic: No PWR led, ACT led very dim and gets hot! (A+)
Replies: 40
Views: 1106

Re: No PWR led, ACT led very dim and gets hot! (A+)

I assume that, according to what you wrote, the MOSFET switching the H-bridge is different to the one shown "controlling" the 10V-out 2-pin connector. HOWEVER: I think that the MOSFET shown has source and drain either wrongly labelled or actually reversed. Bad move. More seriously, it is bad practis...
by davidcoton
Fri Oct 20, 2017 7:58 pm
Forum: Troubleshooting
Topic: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT
Replies: 12
Views: 295

Re: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT

That looks more promising. You will need to remove the link between JD-Vcc and Vcc, then connect JD-Vcc to 5V and Vcc to 3V3. That will run the relays at 5V and the opto-isolator inputs at 3V3, which is Pi-safe. Some relay boards wired as thta one appears to be won't switch on from 3V3, if this is a...
by davidcoton
Fri Oct 20, 2017 7:36 pm
Forum: Troubleshooting
Topic: induction problem gpio relay load
Replies: 34
Views: 2012

Re: induction problem gpio relay load

Forgive me for being dense, but it appears to me that the power to the solenoids (black and white wires, left hand side of thr Relay.jpg picture) is coming directly from a transformer. If so, then it's AC, not DC. Hmm, I didn't notice that. It would be well to check -- do not use diodes across sole...
by davidcoton
Fri Oct 20, 2017 3:24 pm
Forum: Troubleshooting
Topic: i2c with MCP23016 - can´t see connected
Replies: 7
Views: 156

Re: i2c with MCP23016 - can´t see connected

Yep, not good. Sit down first, then read the datasheet.

Pins 1, 8, and 19 to ground. Not just one of them.
Need a clock RC circuit on pin 9.
Need to set the address on pins 16,17,18 -- though you might get a default of 000 or 111 if they float. Or maybe not.

Those three changes for starters.
by davidcoton
Fri Oct 20, 2017 3:09 pm
Forum: Troubleshooting
Topic: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT
Replies: 12
Views: 295

Re: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT

I can understand the relay partly turning off it the GPIO is set to input as the pin will be floating in an undetermined state. Looking at that picture, the relay board doesn't have an opto-isolator/coupler, so you don't have to worry about that, but it is possible it needs a 5V signal which the Pi...
by davidcoton
Fri Oct 20, 2017 1:25 pm
Forum: Troubleshooting
Topic: Pi 3 blinking power led (even no voltage drops)
Replies: 2
Views: 83

Re: Pi 3 blinking power led (even no voltage drops)

What is tthe current limit of you PSU? The Pi3B needs more current than the older models. Where are you measuring the voltage? What peripherals are connected to the PI, particularly USB? An old style spinning hard disk will use substantial current Unless you arrange to trigger your oscilloscope from...
by davidcoton
Fri Oct 20, 2017 1:16 pm
Forum: Troubleshooting
Topic: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT
Replies: 12
Views: 295

Re: Weird relay behaviour: always on if GPIO is set to OUTPUT, kinda turns off if GPIO is set to INPUT

I can't tell from the photo whether the relay board has a transistor (should be OK, should be active high input) or opto-isolator input. If it has an opto-isolator, it doesn't have a 3V3 connection, so it is likely that the input is referenced to 5V. THIS CAN DAMAGE THE PI'S GPIOS. It would also pos...
by davidcoton
Fri Oct 20, 2017 1:04 pm
Forum: Troubleshooting
Topic: induction problem gpio relay load
Replies: 34
Views: 2012

Re: induction problem gpio relay load

Since the soleniods are running on DC, you can also use a reverse parallel diode across the soleniod. Mount it as close to the soleniod as possible. Try this before putting a capacitor across the relay contacts. Diode: 1N4001 should do, others in that series also suitable. Capacitor: Try 0.1μF or 0....
by davidcoton
Thu Oct 19, 2017 11:36 pm
Forum: Troubleshooting
Topic: Ethernet slower than internal wifi?
Replies: 9
Views: 314

Re: Ethernet slower than internal wifi?

What else is the Pi doing, particularly on USB? The on-board Ethernet is connected via a single shared USB port.
by davidcoton
Wed Oct 18, 2017 8:36 am
Forum: Beginners
Topic: GPIO Interaction
Replies: 8
Views: 210

Re: GPIO Interaction

Apart from the plug side of the PSU, there is nothing on a normally working Pi that will give you a shock. The highest voltage is 5V. (Note that is enough to damage other parts of the Pi, as Dougie has said.)
by davidcoton
Tue Oct 17, 2017 11:19 pm
Forum: Troubleshooting
Topic: RetroPie will not load ROMS to 3.5" TFT / Emulation Station Works
Replies: 2
Views: 105

Re: RetroPie will not load ROMS to 3.5" TFT / Emulation Station Works

mikemezaphoto wrote:
Tue Oct 17, 2017 10:45 pm
Figured it out!
Would you care to tell us the solution? Then anyone reading your thread gets the answer without having to ask the question again.
by davidcoton
Tue Oct 17, 2017 11:16 pm
Forum: Beginners
Topic: Executing a pyton script on lighttpd webserver
Replies: 4
Views: 112

Re: Executing a pyton script on lighttpd webserver

skh3llboy wrote:
Tue Oct 17, 2017 10:17 pm
I am not entirely concerned about the security issues .
You should be concerned. Designing security into your projects is an important part of learning about computing.
by davidcoton
Tue Oct 17, 2017 11:14 pm
Forum: Beginners
Topic: Mobile Pi problems (Power, mostly.)
Replies: 2
Views: 89

Re: Mobile Pi problems (Power, mostly.)

One: I KNOW the Pi's 3.5mm output for audio is practically unpowered as is, so passive speakers are pretty much out of the picture. But powered speakers would require me to tap into the already limited power supply. Short of adding in a -second- battery bank simply for the speakers, is there a way ...
by davidcoton
Tue Oct 17, 2017 10:58 pm
Forum: General discussion
Topic: Switching (and wiring) a relay from Python
Replies: 23
Views: 608

Re: Switching (and wiring) a relay from Python

Reverse EMF comes from the energy stored in a coil's magnetic field. When the supply is removed, the field collapses, and the energy is converted back to electricity. If the circuit is open, it reaches a very high voltage -- enough to cause arcs across contacts. The diode will provide a low impedanc...
by davidcoton
Tue Oct 17, 2017 9:23 pm
Forum: General discussion
Topic: Switching (and wiring) a relay from Python
Replies: 23
Views: 608

Re: Switching (and wiring) a relay from Python

I assume that now the relay functions I don't need any resistors between the low voltage side and the Pi? Correct. Can the diode go straight in the terminals of the relay when I wire in the 12V to prevent flowback? The back EMF is generated at the magnet, so across the magnet coil is the best place...
by davidcoton
Tue Oct 17, 2017 5:42 pm
Forum: General discussion
Topic: Pi 3 B As VPN Server: Poor Performance?
Replies: 2
Views: 186

Re: Pi 3 B As VPN Server: Poor Performance?

My research that I have done up until now points towards the pi running it's network communications through what can be simply described as an ethernet to USB adapter as the network communications (or so I'm told) are just run on the USB bus instead of directly on a network bus separate from USB. C...
by davidcoton
Mon Oct 16, 2017 9:44 pm
Forum: Advanced users
Topic: HID works on one Pi Zero, but not another?
Replies: 4
Views: 160

Re: HID works on one Pi Zero, but not another?

Lesson 1. Take a backup before you deploy a system.

I know that doesn't help now, but it should prevent the same problem in the future.
by davidcoton
Mon Oct 16, 2017 6:34 pm
Forum: Troubleshooting
Topic: Problem with starting RPi, U13, and USB
Replies: 1
Views: 32

Re: Problem with starting RPi, U13, and USB

Do you have the necessary skills and equipment to solder SMT parts on an RPi?
If yes -- you can probably replace U13 and the possibly damaged parts around it.
If no -- sorry, just buy another Pi.

Note that there is no full schematic or BOM for the recent Pi models.
by davidcoton
Mon Oct 16, 2017 6:17 pm
Forum: Beginners
Topic: Is it possible to connect more than 5V to ground? <-- Warning Nonsense!
Replies: 18
Views: 649

Re: Is it possible to connect more than 5V to ground? <-- Warning Nonsense!

The tricky bit is ensuring that the signals between subsystems are at a voltage that is both safe and effective on both sides -- your Pi GPIO pins are designed to work at 3.3V, if you connect them to 5V or more your Pi will have serious problems. That said, it is very common for a subsystem running...

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