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by Tage
Sun Nov 03, 2013 3:10 pm
Forum: Automation, sensing and robotics
Topic: Noise from Rasp introduced in OP-AMP or ADC?
Replies: 5
Views: 1316

Re: Noise from Rasp introduced in OP-AMP or ADC?

you probably have a high leakage current from the power supply. switch mode power supplies always have some high frequency currents in addition to the 50Hz line frequency leakage currents. when the output of the power supply is not grounded most of this leakage current can travel through cables to o...
by Tage
Sun Nov 03, 2013 2:58 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: UART TX and open drain
Replies: 7
Views: 2940

Re: UART TX and open drain

you don't need a bidirectional level shifter. replace it with an npn transistor such as 2N3904. connect base to 3.3V through a 10k resistor, emitter to Pi GPIO pin and collector to the high voltage bus that has its own pullup. by the way, the schematic of the bidirectional level shifter is showing 2...
by Tage
Sun Nov 03, 2013 5:18 am
Forum: Advanced users
Topic: Simple A to D to monitor voltage
Replies: 50
Views: 47805

Re: Simple A to D to monitor voltage

I tested my idea to build a simple ADC using a comparator and found that it works. I am using GPIO18 to generate a 100Hz PWM signal which is filtered and applied to one comparator input. the other comparator input is connected to a 12V battery that I want to monitor, through a voltage divider. the c...
by Tage
Fri Nov 01, 2013 1:39 am
Forum: Advanced users
Topic: Simple A to D to monitor voltage
Replies: 50
Views: 47805

Re: Simple A to D to monitor voltage

many times, an Analog to Digital converter is overkill. what you want is a way to detect when the battery voltage has reached a certain level. for example 14.2V. when this happens you want to stop charging, so your battery does not overcharge. so you disconnect the solar panel from the battery. then...
by Tage
Fri Nov 01, 2013 1:26 am
Forum: General discussion
Topic: Simple Power Question (Passing Power to Peripherals)
Replies: 7
Views: 765

Re: Simple Power Question (Passing Power to Peripherals)

just replace the polyfuse with a piece of wire. and make sure you have a quality 5V power supply that makes the polyfuse not necessary.
by Tage
Wed Oct 30, 2013 7:14 pm
Forum: Automation, sensing and robotics
Topic: Input GPIO connect IR Sensor max V/A
Replies: 1
Views: 1265

Re: Input GPIO connect IR Sensor max V/A

Hi all, I am beginner in electronic/robotic and i decided to start a small project which consist in use a small python program to read state of an IR barrer. I bought this one http://www.velleman.eu/products/view/?country=be&lang=en&id=370368 and i never used any GPIO connection on the raspberry pi...
by Tage
Wed Oct 30, 2013 1:37 am
Forum: Beginners
Topic: Need help setting up battery supply
Replies: 5
Views: 1108

Re: Need help setting up battery supply

one of the simplest and cheapest ways to power the Pi from a 12V battery is to get one of these (or something similar) http://www.frys.com/product/1916056?site=sr:SEARCH:MAIN_RSLT_PG then invest your life savings in one of these http://www.frys.com/product/7088931?site=sr:SEARCH:MAIN_RSLT_PG dependi...
by Tage
Mon Oct 28, 2013 2:51 pm
Forum: Automation, sensing and robotics
Topic: Control a simple DC-Motor
Replies: 8
Views: 2675

Re: Control a simple DC-Motor

what for transistors do i need? the simplest way to control a small dc motor is to use two n-channel MOSFETs and two power resistors. connect Source to GND, Gate to an IO pin and the resistor from 5V to Drain. connect the second MOSFET and resistor in the same way, but use a different IO pin for th...
by Tage
Fri Oct 25, 2013 12:49 am
Forum: Networking and servers
Topic: building a nas need help with 4x20 lcd
Replies: 3
Views: 1480

Re: building a nas need help with 4x20 lcd

I am building a has and am having trouble connecting a 4x20 LCD to keep I eye on system info (IP address,storage used/left data up/down ect) any help will be fantastic thanks NIkki if you want help you have to tell what type of LCD display you have. is it using parallel interface, SPI, I2C or UART?...
by Tage
Thu Oct 24, 2013 1:02 am
Forum: General discussion
Topic: phone battery pack used as a battery backup
Replies: 11
Views: 2752

Re: phone battery pack used as a battery backup

Has anyone found/used a battery pack that has a 1.5A or 2.0A output? The first one I picked up only has 1A and I'm having issues when USB devices are connected. there is no such thing as a battery that has 1.5A output. or 2 A output. a phone battery typically is a single cell Li-Ion with 3.6V nomin...
by Tage
Thu Oct 24, 2013 12:58 am
Forum: General discussion
Topic: hello
Replies: 2
Views: 476

Re: hello

Hi everyone, im new and had a question or two about supplying power to the pi. I have two li-on 7.4 2200 mah 16.3wh batteries and a voltage regulator. So I was wondering how much power that would give me and how would I charge them(what type of charger to use) with this type of battery chemistry yo...
by Tage
Tue Oct 22, 2013 2:19 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Measured Relay Specs
Replies: 5
Views: 1698

Re: Measured Relay Specs

if you are very concerned about power usage, a relay is a very bad idea. it is better to try to implement the function with a MOSFET. a MOSFET does not require any power at all on the control input. all it takes is to apply a voltage to the gate. if you have to use a conventional relay, you can take...
by Tage
Tue Oct 22, 2013 2:04 am
Forum: General discussion
Topic: Is this voltage regulator working?
Replies: 8
Views: 1597

Re: Is this voltage regulator working?

Additional details: I fed it 9.38v off of 6 AA batteries. When I plugged it in the first time, I think I saw a wisp of smoke and the regulator got quite hot. I unplugged it and tried again later, which is where I got the 3v reading. if you see a wisp of smoke when plugging something in, that is a s...
by Tage
Tue Oct 22, 2013 1:56 am
Forum: General discussion
Topic: Is this voltage regulator working?
Replies: 8
Views: 1597

Re: Is this voltage regulator working?

FWIW (and for the curious) ~30 years ago, as a young physicist, I made some notes w.r.t. linear PSU design and, subsequently, built a multi-rail PSU based upon those ideas and incorporating early versions of what became the generic "78xx" series of regulators. The notes can be found here: http://ww...
by Tage
Fri Oct 18, 2013 2:24 pm
Forum: Troubleshooting
Topic: About microUSB polyfuse of Model B.
Replies: 20
Views: 14052

Re: About microUSB polyfuse of Model B.

I largely agree, but the adding of a polyfuse (of this current value) may have been not a technical discussion but a legal one. I know that Farnell has a large legal department, that had a large influence on the design (think EMC testing for example). also, why do you think a real fuse would be bet...
by Tage
Thu Oct 17, 2013 4:44 am
Forum: Troubleshooting
Topic: About microUSB polyfuse of Model B.
Replies: 20
Views: 14052

Re: About microUSB polyfuse of Model B.

I have three Pi, two are made in China, one is made in UK. the ones made in China has a polyfuse marking T075, the one made in UK has a marking 7V, this marking is double, it can be read upside down or right way up. The device with the distinctive overlapping "V" symbol is a Tyco Electronics (Raych...
by Tage
Thu Oct 17, 2013 3:16 am
Forum: Troubleshooting
Topic: About microUSB polyfuse of Model B.
Replies: 20
Views: 14052

Re: About microUSB polyfuse of Model B.

I have three Pi, two are made in China, one is made in UK. the ones made in China has a polyfuse marking T075, the one made in UK has a marking 7V, this marking is double, it can be read upside down or right way up. perhaps before we start discussing the poly fuse specification we should agree on th...
by Tage
Wed Oct 16, 2013 1:56 pm
Forum: Troubleshooting
Topic: About microUSB polyfuse of Model B.
Replies: 20
Views: 14052

Re: About microUSB polyfuse of Model B.

The holding current is the maximum current - at room temperature - that you should be able to run through the polyfuse without activating it. if the circuit board is at a higher temperature the polyfuse will certainly trip at a much lower current. don't expect more than about 500mA at +40C if the no...
by Tage
Sat Oct 12, 2013 3:31 pm
Forum: Other projects
Topic: 100% solar powered Pi?
Replies: 8
Views: 43709

Re: 100% solar powered Pi?

I agree that some trial and error is necessary. But it is always good to try to calculate the panel size and battery before investing money. I have an interest in this myself as I am trying to set up a surveillance system for my motorhome. Ideally, the motorhome should call me if somebody tries to b...
by Tage
Sat Oct 12, 2013 1:40 am
Forum: Other projects
Topic: 100% solar powered Pi?
Replies: 8
Views: 43709

Re: 100% solar powered Pi?

I want to make my Pi be 100% solar powered. I'm no electrician so bear with me on this. Ive read that the Pi uses about 48Wh a day, which equates to about 9.6Amps at 5 volts. With the minimum requirement for the pi being about 700-1000mA, would I be able to power a Pi off using a 12W panel @ 6 volt...
by Tage
Sun Oct 06, 2013 2:15 am
Forum: Automation, sensing and robotics
Topic: 24VAC to 5VDC Conversion
Replies: 15
Views: 16570

Re: 24VAC to 5VDC Conversion

The factor is 1.414 (squareroot from 2), not 1.7 - so you reach at maximum around 34V ... And you have also to subtract voltage across diodes, so a little bit less than this value ... MfG, FM_81 that is not true in real life. at all. you can expect mains voltage variations and you need to take thos...
by Tage
Sat Oct 05, 2013 7:47 pm
Forum: Automation, sensing and robotics
Topic: 24VAC to 5VDC Conversion
Replies: 15
Views: 16570

Re: 24VAC to 5VDC Conversion

if you are using a 24Vac transformer and you add a rectifier bridge and a capacitor to convert the ac voltage to dc, then you must consider that the dc voltage occasionally can go above 40V. so at least one of not both of the dc/dc converters mentioned are not suitable. one has 18V rating the other ...
by Tage
Sat Oct 05, 2013 1:01 am
Forum: Automation, sensing and robotics
Topic: Power supply
Replies: 2
Views: 491

Re: Power supply

1. get a 12V battery. the size depends on your application. Sealed Lead Acid is cheapest. 2. get a 12V-to-5V 1A plug of the type that has a USB connector and is used to charge cell phones from a car cigarette lighter. it will cost you about $5. 3. figure out how to wire it all together 4. figure out...
by Tage
Fri Oct 04, 2013 1:21 am
Forum: Automation, sensing and robotics
Topic: Plants watering system
Replies: 2
Views: 795

Re: Plants watering system

I would not recommend messing around with mains voltage and unlimited supply of water, especially not combined. I would start with a good quality 12V power supply and power anything that is connected to the Pi from that supply. Then I would use a water container that only can hold a limited amount o...
by Tage
Fri Oct 04, 2013 1:13 am
Forum: Beginners
Topic: Battery Power for Portable Pi
Replies: 9
Views: 1273

Re: Battery Power for Portable Pi

I would use any 12V battery and buy one of those gadgets that plug into the cigarette lighter and provide 5V at 1A or more to a USB connector. I usually open the gadget and throw away the enclosure and other unnecessary stuff and use only the circuit board. the cost is only a few dollars. you can ev...

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