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by Tage
Tue Apr 08, 2014 2:43 pm
Forum: General discussion
Topic: Solar powered pi
Replies: 4
Views: 1124

Re: Solar powered pi

this may give you some idea: where I live (San Francisco area) we get 6kWh per m2 per day in April. this is the amount of sunlight that hits the panel if it is pointed towards south with the correct angle. the panel efficiency is about 15% (at +25C) but you need to compensate for the fact that the p...
by Tage
Thu Mar 27, 2014 1:48 am
Forum: General discussion
Topic: Rasberry Pi Solar Charger
Replies: 18
Views: 2635

Re: Rasberry Pi Solar Charger

I'm looking to turn my boat pi into a solar camping pi this year. Something that can bootstrap the beginner would be excellent. People keep going on about solar but being able to hook up multiple DC inputs would be nice. Wind and solar? And able to attach your own battery? With both power and data ...
by Tage
Thu Mar 27, 2014 1:35 am
Forum: Off topic discussion
Topic: Canon EOS Rebel ?
Replies: 2
Views: 1696

Re: Canon EOS Rebel ?

these are all good cameras. I am a photographer in my spare time. you live in a very beautiful place and should get a camera!
I recommend http://www.dpreview.com/ if you want advice on cameras and such. this is not the right forum
by Tage
Wed Mar 26, 2014 2:27 pm
Forum: Other projects
Topic: Relay for motorized valve
Replies: 13
Views: 3083

Re: Relay for motorized valve

Tage -- 2 more questions: 1. Why is R1 necessary? 2. Could a transistor do the same job as the mosfet is doing in the circuit? Sorry for bugging you with so many questions. I hope you don't mind too much. Thanks. R1 is used to keep the gate-source voltage at zero when the npn transistor is not ON. ...
by Tage
Wed Mar 26, 2014 2:10 am
Forum: Automation, sensing and robotics
Topic: hot tub
Replies: 15
Views: 7890

Re: hot tub

Interesting project. I am an electrical engineer, and fairly familiar with the hazards of power electronics. I have to STRONGLY WARN against using any relay boards bought off the internet or otherwise for projects like this! the problem is that many relay boards I have seen are totally unfit to be u...
by Tage
Tue Mar 25, 2014 7:29 pm
Forum: Other projects
Topic: Relay for motorized valve
Replies: 13
Views: 3083

Re: Relay for motorized valve

Hello Tage -- Was wondering if you could help me with a few question I have. I wanted to explore running this with a transistor option a little bit. I have read up on transistor and it definitely sounds like a better option. But I am not sure how to hook all the wires up from this valve. All the tr...
by Tage
Mon Mar 24, 2014 3:20 pm
Forum: General discussion
Topic: Rasberry Pi Solar Charger
Replies: 18
Views: 2635

Re: Rasberry Pi Solar Charger

as an example, where I live (San Francisco area) we get 6kWh per m2 per day in April. this is the amount of sunlight that hits the panel if it is pointed towards south with the correct angle. the panel efficiency is about 15%, but you need to compensate for the fact that the panel heats up. to run a...
by Tage
Sat Mar 22, 2014 3:26 pm
Forum: Other projects
Topic: Relay for motorized valve
Replies: 13
Views: 3083

Re: Relay for motorized valve

you can probably do it with a transistor, but a relay also works. there is not much information on the website. it is possible that you can connect the GND to +12V and the POWER lead to GND, as this device can take ac voltage. if that is the case you could replace the contact with an npn or nmos tra...
by Tage
Tue Mar 18, 2014 2:20 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Using 2n2222a as a switch for IR LEDs
Replies: 9
Views: 7181

Re: Using 2n2222a as a switch for IR LEDs

2N2222 is not suitable. you will need more base current than what the Pi can deliver to drive 300mA load. The base-emitter voltage drop will be about 1V, and you need over 20mA base current to avoid that the transistor overheats because it goes out of saturation. A better choice is an n-channel MOSF...
by Tage
Sun Mar 16, 2014 3:24 pm
Forum: Automation, sensing and robotics
Topic: solenoid help
Replies: 4
Views: 760

Re: solenoid help

this seems to be a 220Vac coil, so you need a relay that can handle mains voltage. you could get one with a 5V coil, so you just need a transistor to drive it. be careful when buying relay boards, because apparently there are many that are not suited for connection to the mains voltage. the boards h...
by Tage
Mon Mar 10, 2014 3:40 pm
Forum: Off topic discussion
Topic: Question about power supplies (not for a Pi)
Replies: 17
Views: 2634

Re: Question about power supplies (not for a Pi)

look at the label of the power supply. in the lower right corner you will see the polarity indicator. it shows the normal polarity for this type of connector. the outer surface is GND and the inside is +5V. when you buy a replacement you can get one that fits a different size pin ( the hole can be f...
by Tage
Sun Mar 09, 2014 5:21 pm
Forum: Automation, sensing and robotics
Topic: Help with the use of a transistor
Replies: 2
Views: 1342

Re: Help with the use of a transistor

connect the emitter to GND pin on the GPIO header replace the LED with a resistor (for example 10k) that is connected to 3.3V pin on the GPIO header connect the collector to a GPIO pin of your choice. when the signal from the door bell turns ON the transistor, the collector voltage drops to 0V and y...
by Tage
Tue Mar 04, 2014 3:16 pm
Forum: General discussion
Topic: How can I power a lab of Pis?
Replies: 17
Views: 3767

Re: How can I power a lab of Pis?

I would not recommend to use a 30A 5V supply to power 25 Pi boards, you would need a fuse for each USB cable because a damaged cable can catch fire if you have a 30A supply with current limit feeding it. the fuse will cause problems with voltage drops so you will have too low voltage at the Pi. and ...
by Tage
Sun Mar 02, 2014 3:19 pm
Forum: Troubleshooting
Topic: Exploding Pi
Replies: 28
Views: 6020

Re: Exploding Pi

This is why I am saying that nobody should buy anything that is plugged into the mains outlet from cheap internet sources. (but how do you know when even Amazon is guilty?).

never connect a relay board you bought online to the mains voltage without having an electrical engineer checking it out!
by Tage
Sun Feb 09, 2014 3:59 pm
Forum: General discussion
Topic: How many millamps is needed to power raspberry pi and screen
Replies: 8
Views: 1270

Re: How many millamps is needed to power raspberry pi and sc

Thanks for the reply. I haven't bought the screen yet. Here is the link to it: http://www.amazon.co.uk/gp/product/B007SLDF7O/ref=ox_sc_act_title_8?ie=UTF8&psc=1&smid=A1UUT617FH3AUB I am using a Raspberry Pi model B. Also here is the link to the battery that I think would be needed: http://www.amazo...
by Tage
Tue Feb 04, 2014 4:11 am
Forum: Other projects
Topic: Relay for solenoid... help needed!
Replies: 6
Views: 2359

Re: Relay for solenoid... help needed!

if you have only 3.3V available to drive 1A, the Sparkfun and Adafruit MOSFETs in TO-220 package is not so great. the descriptions and claims in the advertisements are a bit misleading. people are confused by the gate threshold voltage spec. instead i would recommend MOSFET that has really low gate ...
by Tage
Tue Feb 04, 2014 2:48 am
Forum: Off topic discussion
Topic: Solar Panel Battery Charger... question about circuit...
Replies: 7
Views: 3720

Re: Solar Panel Battery Charger... question about circuit...

a common solar panel is built form a number of series connected solar cells. if you take a voltmeter and measure the voltage when there is no load and the sun is shining on the panel you will get a reading, this is the open circuit voltage (Voc). you can connect several of these solar panels in seri...
by Tage
Mon Feb 03, 2014 3:52 pm
Forum: Troubleshooting
Topic: Relay control with GPIO pins
Replies: 12
Views: 2705

Re: Relay control with GPIO pins

the misunderstanding that a dc relay has an inrush current may be related to that a relay requires a lot more current (voltage on the relay coil) in order to activate (close the contacts) than what is required to keep the relay activated. the current in the relay coil is determined by the resistance...
by Tage
Fri Jan 31, 2014 3:34 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Switching power: high side or low side?
Replies: 19
Views: 5453

Re: Switching power: high side or low side?

ada.png if you are going to use this MOSFET you need a 5V micro controller to drive it. if you drive it directly you should put at least 100ohm to 1k in series with the gate because the MOSFET has a quite large gate capacitance that will cause some current spikes in the GPIO. the Adafruit informati...
by Tage
Tue Jan 28, 2014 3:48 pm
Forum: General discussion
Topic: Voltage regulator
Replies: 4
Views: 849

Re: Voltage regulator

http://www.linear.com/demo/DC1523A the simplest way is to get a demo board for LTC3789 and remove R25. this will increase the current limit to 10A (in the input range 9V to 36V). the board delivers 12V but you can adjust the output voltage by increasing RFB1. If you want 19V you also need to replace...
by Tage
Mon Jan 27, 2014 1:59 am
Forum: General discussion
Topic: How many solar panels would i need to power
Replies: 13
Views: 3289

Re: How many solar panels would i need to power

Hi, i have 5 6V 120mA Solar Panels. How many of those solar panels would i need to power the pi and what would be the best way, IE hooked up to a battery. What would be the best battery etc my guess is that you will need at least a 60W solar panel, probably more. and you need a large battery if you...
by Tage
Sat Jan 25, 2014 2:19 am
Forum: Automation, sensing and robotics
Topic: PiFace: High Voltage/Amperage Relay Board?
Replies: 8
Views: 4137

Re: PiFace: High Voltage/Amperage Relay Board?

In the name of keeping things simple and, as you put it "ease of wiring," avoid the DIY Relay circuit and go for a pre-manufactured relay board such as this one: http://www.ebay.com/itm/New-Style-5V-4-Channel-Relay-Module-Switch-Board-For-Arduino-PIC-ARM-AVR-DSP-PLC-/360718037491?pt=LH_DefaultDomai...
by Tage
Wed Jan 22, 2014 2:05 am
Forum: Troubleshooting
Topic: Serial LCD does not work in bash
Replies: 6
Views: 1055

Re: Serial LCD does not work in bash

first, try to insert some delays in your code for troubleshooting purpose. second, after inserting the delays and it did not work, add an npn transistor as level shifter. at the display data input, use a 10k pullup resistor from the display RX pin to 5V. and at the Pi, a npn transistor with emitter ...
by Tage
Tue Jan 07, 2014 2:10 am
Forum: General discussion
Topic: Voltage Meter
Replies: 8
Views: 1659

Re: Voltage Meter

for a really low cost solution you could purchase two STM32F4discovery boards ($15 each) and use their 12bit analog to digital inputs. the simplest way that I know of is to use Espruino (use google). connect to the Cortex M4 boards using serial interface (UART) or USB. you could manage with one of t...

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