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by Tage
Sun Jan 05, 2014 4:13 pm
Forum: Advanced users
Topic: 25W Power supply
Replies: 17
Views: 7151

Re: 25W Power supply

BBZ.png it is always worth checking any power supply before connecting it to the Pi. with a large power supply I would measure the output voltage at no load, and even check that the voltage does not shoot up when the Pi is unplugged, as this causes overvoltage to the Pi if it is plugged back in whi...
by Tage
Sat Jan 04, 2014 3:54 pm
Forum: Automation, sensing and robotics
Topic: Simple transistor question
Replies: 7
Views: 1421

Re: Simple transistor question

danjperron and others already gave detailed answers, I would just like to add this: the dc current gain hFE is specified with 5V across the transistor. this is not what we want in this case. we want the transistor to saturate, so it does not dissipate a lot of power. so we cannot use even the minimu...
by Tage
Fri Jan 03, 2014 8:16 pm
Forum: Beginners
Topic: Servo goes crazy with transistor
Replies: 16
Views: 3512

Re: Servo goes crazy with transistor

the IRF630 only has a 10V specification for Rdson, so it is not suitable when the gate voltage is only less than 3.3V. it is a common beginners mistake to look only at the gate threshold spec (2V to 4V in this case) and forget that this threshold voltage is specified at very low drain current. when ...
by Tage
Fri Jan 03, 2014 3:05 pm
Forum: Beginners
Topic: Servo goes crazy with transistor
Replies: 16
Views: 3512

Re: Servo goes crazy with transistor

The problem with the dc motor driver heating up is that there is not enough gate voltage when driving from 5V. connect the collector of the optocoupler to 12V instead. the most natural thing would be to get an n-channel MOSFET that has lower gate threshold and drive it directly from the GPIO as in y...
by Tage
Thu Jan 02, 2014 8:21 pm
Forum: Beginners
Topic: Servo goes crazy with transistor
Replies: 16
Views: 3512

Re: Servo goes crazy with transistor

5Vdriver.png you could try to place the power switch in the +5V line and connect the servo GND to GND. I would think that the servo electronics receives some current with the ground lead floating and the signal lead connected to a lower voltage than 5V. Do you mean exactly like the diagram? I've pl...
by Tage
Thu Jan 02, 2014 3:49 pm
Forum: Beginners
Topic: Servo goes crazy with transistor
Replies: 16
Views: 3512

Re: Servo goes crazy with transistor

5Vdriver.png
5Vdriver.png (18.85 KiB) Viewed 3442 times
you could try to place the power switch in the +5V line and connect the servo GND to GND. I would think that the servo electronics receives some current with the ground lead floating and the signal lead connected to a lower voltage than 5V.
by Tage
Thu Jan 02, 2014 1:25 am
Forum: Beginners
Topic: Power and GPIO pins
Replies: 4
Views: 716

Re: Power and GPIO pins

as far as I know, the layout files have not been released to the public so it is impossible to know how much current the traces can carry and how the GND pin is connected. just looking at the circuit board, it appears that the traces are fairly thin so I would think that you safely can run 1 Ampere ...
by Tage
Wed Jan 01, 2014 2:32 am
Forum: Beginners
Topic: Controlling a DC motor
Replies: 5
Views: 785

Re: Controlling a DC motor

mdrvr.png yes, there are many options if you just want to connect the motors and create a program to watch the motors turn while controlling the speed and direction with software. if you have two transistors and a few resistors you could build this simple motor controller. to run the motor, turn on...
by Tage
Tue Dec 31, 2013 2:11 am
Forum: Beginners
Topic: Stuck: Need switch controled by GPIO
Replies: 30
Views: 3846

Re: Stuck: Need switch controled by GPIO

there is no need to connect a resistor across the npn if you have the pullup resistor to 5V. the gate will not be floating.it is connected to the 5V supply through the pullup. when the 5V supply goes down it brings the gate voltage with it. you could have any resistor value for the pullup resistor (...
by Tage
Mon Dec 30, 2013 3:46 pm
Forum: Beginners
Topic: Stuck: Need switch controled by GPIO
Replies: 30
Views: 3846

Re: Stuck: Need switch controled by GPIO

there is one error in your schematic. move R2 so that it connects to 5V and connect the collector directly to the gate.
when the npn is off, the gate is pulled to 5V by R2 and the LEDs are lit.
to turn off the LEDs, set the GPIO high.
by Tage
Fri Dec 27, 2013 3:10 pm
Forum: Automation, sensing and robotics
Topic: AC motor connected to Raspberry Pi
Replies: 6
Views: 3821

Re: AC motor connected to Raspberry Pi

The motor current can be up to 7Arms which translates into 1400W. it is better to use a motor drive that is powered from the mains voltage than to try to boost the voltage from 12Vdc to a high ac voltage that can be fed to the motor drive (inverter). you could purchase a true sinewave inverter that ...
by Tage
Mon Dec 23, 2013 5:04 pm
Forum: Advanced users
Topic: Power from battery pack
Replies: 8
Views: 2595

Re: Power from battery pack

the datasheet for this product does not have much content. it is a quite useless document. from the physical dimensions I would guess that it contains an 18650 cell (3.7V), so the 2200mAh capacity number is probably for the cell and not for the 5V output. you could try to load the output and measure...
by Tage
Mon Dec 23, 2013 4:40 pm
Forum: General discussion
Topic: Motor circuit suggestions
Replies: 5
Views: 1184

Re: Motor circuit suggestions

point C (the emitter of the transistor in this case) should be connected both to Pi GND (so the base-emitter current can return to the 5V supply) and to the negative terminal of you battery (so the motor current through the collector-emitter can return to the battery). I assume you have a diode conn...
by Tage
Sun Dec 22, 2013 4:38 pm
Forum: General discussion
Topic: 12V 7.2Ah lead acid battery charging question.
Replies: 17
Views: 10469

Re: 12V 7.2Ah lead acid battery charging question.

sounds like you also need proper cut-off systems, to cut power if you go below 10volts Would two LM2596S perform this task? RaspPi <--> LM2596S set at 5 Volts <--> LM2596S set at 10 Volts <--> 12 Volt battery The first LM2596S ensures that the RaspPi is getting 5 Volts The second LM2596S ensures th...
by Tage
Sat Dec 21, 2013 3:35 pm
Forum: Troubleshooting
Topic: RPi crashes (sometimes) when I connect a USB peripheral
Replies: 15
Views: 4225

Re: RPi crashes (sometimes) when I connect a USB peripheral

get a large electrolytic capacitor and connect it across the 5V and GND on the Pi, wherever you can find a suitable place to solder the wires. for example, a 10.000uF 6.3V radial aluminum electrolytic capacitor will cost you about $1. a smaller one may also work well. the main problem is the lack of...
by Tage
Sat Dec 21, 2013 1:14 am
Forum: General discussion
Topic: LCD screen power options?
Replies: 4
Views: 3105

Re: LCD screen power options?

it seems that the display is using a buck-regulator that operates from 6V minimum. this indicates that the output voltage is 5V, so if you manage to find the schematic for the board you may be able to figure out where to connect 5V from the Pi. you may have to remove the input capacitor to the buck ...
by Tage
Fri Dec 20, 2013 4:09 am
Forum: Beginners
Topic: Controlling a solenoid
Replies: 13
Views: 4282

Re: Controlling a solenoid

the typical pinout is EBC
check your connections again. it looks like you grounded you base and have also other mistakes. where is the collector and emitter wired?
by Tage
Mon Dec 16, 2013 2:34 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Loading Cortex M4's
Replies: 7
Views: 2168

Re: Loading Cortex M4's

I don't know what I am talking about, but try googling "espruino" and "micro python"
by Tage
Sat Dec 14, 2013 3:00 pm
Forum: Automation, sensing and robotics
Topic: Controlling 12VDC from GPIO
Replies: 25
Views: 14004

Re: Controlling 12VDC from GPIO

a schematic sketch would make it easier, it appears that you have the relay connected correctly. you are talking about a "latch", what is that? if you are trying to control a latching relay you may need a special circuit configuration. if you have a conventional relay you just have to keep checking ...
by Tage
Fri Dec 13, 2013 8:23 pm
Forum: Beginners
Topic: Solar Powered Pi (Model A)
Replies: 1
Views: 416

Re: Solar Powered Pi (Model A)

the main problem is that the Pi is really power hungry and the sun is unreliable. it always shines but not where you want it to 8-) I had a look at websites that talk about off grid solar power systems which is basically what you are thinking of. one difference is that when you have a small cabin of...
by Tage
Tue Dec 10, 2013 9:24 pm
Forum: Advanced users
Topic: FET Source-Gate Charge & Back-current
Replies: 3
Views: 1034

Re: FET Source-Gate Charge & Back-current

I don't believe there is a risk that the Pi is damaged by the current spikes when the GPIO pin is switching, as long as you use a resistor between the GPIO pin and the Gate to limit the peak current. the GPIO circuitry is what is driving the current transients. one thing to look out for is the possi...
by Tage
Tue Dec 10, 2013 2:49 am
Forum: Off topic discussion
Topic: How to measure amps of a solar panel
Replies: 19
Views: 15057

Re: How to measure amps of a solar panel

the way to measure amps of a solar panel is to connect an amperemeter to the wires. this will give the short circuit current value for the solar panel. the important thing to understand is that the current is proportional to the amount of sunlight that hits the panel. so to have any meaning you need...
by Tage
Mon Dec 09, 2013 8:16 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: LTC2442 24 bit ADC via spi
Replies: 3
Views: 4924

Re: LTC2442 24 bit ADC via spi

you should contact the manufacturer and ask for drivers for the part. it is likely that there are drivers available that you can use.
for example, http://www.linear.com/product/LTC2442 has some drivers for Arduino
by Tage
Mon Dec 09, 2013 8:11 pm
Forum: General discussion
Topic: Outdoor power
Replies: 22
Views: 7733

Re: Outdoor power

a 12V 12Ah battery has about 12V*12Ah=144Wh capacity. if your Pi and its gadgets draw 4W then the battery will last 144Wh/4W=36h if it is fully charged. in real life if you want to get some decent lifetime from the battery you should not discharge it totally. it will last longer if you recharge afte...
by Tage
Mon Dec 09, 2013 2:46 pm
Forum: General discussion
Topic: Outdoor power
Replies: 22
Views: 7733

Re: Outdoor power

I am aware of the low budget for the project which is why I suggested two batteries that are manually charged and swapped out at regular intervals. The battery should always be a deep discharge battery as been pointed out. a car battery will not last when it is being repeatedly discharged more than ...

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