## Search found 287 matches

Sat Feb 07, 2015 1:59 am
Forum: Automation, sensing and robotics
Topic: Electrical input of a Raspberry Pi over an hour?
Replies: 7
Views: 1450

### Re: Electrical input of a Raspberry Pi over an hour?

to get out of the fog you need to start calculating in Watt hours. assuming your battery has 37Wh capacity (10Ah times 3.7V) and your Pi is sucking 0.75A * 5V = 3.75W in an ideal world your battery would last 37Wh/3.75W =9.8 hours. but you will have power losses in the power converter that converts ...
Sat Feb 07, 2015 1:47 am
Forum: General discussion
Topic: GPIO details and PNP transistors
Replies: 3
Views: 1935

### Re: GPIO details and PNP transistors

if you want to use pnp transistors you should connect emitter to 3.3V and base to GPIO through a resistor. the load is connected from collector to GND. if you know the load current I you can select the resistor value R=10*(3.3V-0.7V)/I to explain the expression: the factor 10 comes from the gain of ...
Thu Feb 05, 2015 3:38 pm
Forum: Off topic discussion
Topic: Salvaging Old Components
Replies: 4
Views: 833

### Re: Salvaging Old Components

M66311P data sheet can be found on the Renesas website. this is a 5V part so you need to add a simple level shifter to the serial input when driving it from 3.3V GPIO. for example, connect a 1N4148 diode from the input pin of M66311P to the GPIO pin of Pi, and add a 10k resistor from the input pin (...
Fri Jan 16, 2015 3:08 am
Forum: General discussion
Topic: Can anyone suggest me a reliable relay board?
Replies: 31
Views: 6870

### Re: Can anyone suggest me a reliable relay board?

that relay is not suitable for an application where the low voltage circuitry is not grounded. your dishwasher is grounded and the low voltage circuitry is not accessible by the user. so it is allowed to use "basic insulation". if you use this type of relay with the Pi and use it to control loads a...
Fri Jan 16, 2015 1:55 am
Forum: Automation, sensing and robotics
Topic: Solar Power, intelligent control using Pi
Replies: 7
Views: 2913

### Re: Solar Power, intelligent control using Pi

perhaps it would make sense to put the extra energy into the hot water heater?
after all, you probably shower now and then.
Wed Jan 14, 2015 8:51 pm
Forum: General discussion
Topic: Can anyone suggest me a reliable relay board?
Replies: 31
Views: 6870

### Re: Can anyone suggest me a reliable relay board?

I would even be careful to buy any relay board that uses relays only specified for 1500V isolation. The relays in my UL/CE approved computer controlled dishwasher are only rated at 2000 volts coil to contacts. http://datasheet.octopart.com/G5LE-1117P-PS-DC6-Omron-datasheet-109984.pdf that relay is ...
Sat Jan 10, 2015 3:58 pm
Forum: Other projects
Topic: pi on a car battery?
Replies: 9
Views: 3718

### Re: pi on a car battery?

I have a different method for calculating how long a certain battery can power a load: Calculate the Watt-hour capacity of the battery by multiplying the nominal battery voltage with the Amperehour capacity, then divide by the number of Watts that the load requires. The battery capacity is often giv...
Mon Jan 05, 2015 3:18 am
Forum: Automation, sensing and robotics
Topic: Which transistors are good for controlling 5 to 12.5v DC
Replies: 19
Views: 3052

### Re: Which transistors are good for controlling 5 to 12.5v DC

http://www. eciaauthorized.com/ this link is what I use when looking for data sheets and cost information. it is almost impossible to get usable search results these days when googling part numbers on the internet. this link is much more useful. I don't agree, searching datasheets is easy, and does...
Sun Jan 04, 2015 4:48 pm
Forum: Automation, sensing and robotics
Topic: Which transistors are good for controlling 5 to 12.5v DC
Replies: 19
Views: 3052

### Re: Which transistors are good for controlling 5 to 12.5v DC

The only type of transistor I can recommend for driving loads that require more than a few hundred milliAmperes is n-channel MOSFETs that have the ON resistance (Rdson) specified at 2.5V gate voltage. It is impossible to find these transistors in packages that contains pins that can be inserted into...
Fri Jan 02, 2015 12:25 am
Forum: Automation, sensing and robotics
Topic: Dimming the lights (MOSFET + digi pot)
Replies: 10
Views: 5744

### Re: Dimming the lights (MOSFET + digi pot)

using a triac and phase control is definitely a good idea if the purpose is to build a dimmer circuit. a triac is very rugged and after it has been triggered by a current pulse into the gate it will stay on during the rest of the half period of the 50Hz/60Hz mains voltage cycle, and it turns off aut...
Thu Jan 01, 2015 5:12 pm
Forum: Automation, sensing and robotics
Topic: Dimming the lights (MOSFET + digi pot)
Replies: 10
Views: 5744

### Re: Dimming the lights (MOSFET + digi pot)

Here is an example of a home built solid state relay. Two MOSFETs are connected with common Source pins and common Gate pins. these two MOSFETs together form an ac switch. current can flow in both directions when a voltage is applied from Gate to Source. An optocoupler is used to provide isolation f...
Sun Dec 28, 2014 6:31 pm
Forum: Beginners
Topic: Electrical Newbie. Cap+resist+relay.
Replies: 14
Views: 1970

### Re: Electrical Newbie. Cap+resist+relay.

here is one suggestion. use a p-channel MOSFET to switch the 5V supply. here is how it works: the MOSFET M1 is off. there is +5V at the source S but the voltage at the drain D is zero because the voltage between gate and source is held at zero by the 10k resistor. Q1 is off. press the push button. w...
Wed Dec 24, 2014 7:58 pm
Forum: Automation, sensing and robotics
Topic: How to read 64 analog signals at the same time.
Replies: 13
Views: 6166

### Re: How to read 64 analog signals at the same time.

Here is one way to set up the test: add a noninverting amplifer for each of the 64 inputs and amplify the signal so the maximum is close to 3.3V. this takes sixteen quad opamps (with low input offset voltage) and 128 resistors. add eight 8-1 analog multiplexers to switch the (amplified) signals in g...
Wed Dec 24, 2014 7:12 pm
Forum: Beginners
Topic: In car power supply.
Replies: 4
Views: 1411

### Re: In car power supply.

the simplest way would be to buy a 12V 7Ah sealed lead acid battery (SLA). this will give you 84Watt hour so you can run your Pi from this battery for almost 24h. if you need to charge the battery while driving you could connect a Schottky diode from the cigarette lighter plug to the SLA battery. yo...
Tue Dec 23, 2014 9:00 pm
Topic: What's the use of U14 (dual PNP transistors) around P-FET?
Replies: 4
Views: 2963

### Re: What's the use of U14 (dual PNP transistors) around P-FE

I think the circuit is controlling the gate voltage ( by controlling the current flow in the 47k resistor) in the way that the p-channel MOSFET is on if Drain is higher than Source (there is a forward voltage on the body diode of the MOSFET), and it turns off if Source is higher than Drain (body dio...
Tue Dec 16, 2014 8:06 pm
Forum: Beginners
Topic: 7.4V/2S 1800mAh 20C LiPo battery for LCD and Raspberry PI
Replies: 10
Views: 5481

### Re: 7.4V/2S 1800mAh 20C LiPo battery for LCD and Raspberry P

the voltage converter should work. adjust the output voltage before connecting it to the Pi, as people already mentioned.. regarding the battery there is not enough information to know what kind of protection circuitry is included. if any. the danger with this type of battery is that it will burst i...
Tue Dec 16, 2014 3:35 pm
Forum: Troubleshooting
Replies: 6
Views: 2773

here is the schematic for a motordrive using two relays and a MOSFET, plus a diode, a fuse and a 12V battery.
connect the gate of the MOSFET to a GPIO pin and use PWM to control the speed of the motor.
turn on one relay for Forward, the other relay for Reverse.
Tue Dec 16, 2014 3:46 am
Forum: Troubleshooting
Replies: 6
Views: 2773

you can probably control the 12V dc motor from the Pi. the only problem is that you need a H-bridge, so you have to do some soldering if you don't want to invest in a motor drive circuit board which is definitely much easier. if you go for a simple H bridge you could use P-channel MOSFETs for the to...
Tue Dec 16, 2014 3:28 am
Forum: Beginners
Topic: 7.4V/2S 1800mAh 20C LiPo battery for LCD and Raspberry PI
Replies: 10
Views: 5481

### Re: 7.4V/2S 1800mAh 20C LiPo battery for LCD and Raspberry P

Greetings, I am working on a project for my final exam of school, its a vocation course of eletronic, automation and computers which has a final exam known as professional aptitude test. What I want to do has already been done with the Raspberry PI, there is a popular video from Ben Heck that shows...
Mon Dec 15, 2014 3:11 pm
Forum: Troubleshooting
Replies: 6
Views: 2773

my suggestion is to get a windshieldwiper motor or car window opener motor and a 12V dc motor controller that allows you to adjust the force as needed, by controlling the maximum motor current. wind shield wiper motor assemblies contain the gearbox, and are very cheap. you would need to fit a belt d...
Mon Dec 08, 2014 1:35 am
Forum: Automation, sensing and robotics
Topic: Saintsmart Solid state relay?
Replies: 6
Views: 2518

### Re: Saintsmart Solid state relay?

Specifications Power supply: 5V DC(160mA) Input control signal voltage: (0-0. 5V low stage SSR is OFF) (2. 5-20V high stage SSR is ON) SSR Output (each channel): Load voltage range: 75 to 264VAC (50/60Hz). Load current: 0. 1 to 2 AMP. Power supply: 5VDC / 160mA (all channel ON). Input control signal...
Fri Dec 05, 2014 2:04 am
Forum: Off topic discussion
Topic: Circuit design software??
Replies: 25
Views: 32177

### Re: Circuit design software??

LTSpice
Fri Dec 05, 2014 2:02 am
Forum: Beginners
Topic: GPS tracker for a drone
Replies: 4
Views: 1539

### Re: GPS tracker for a drone

I would use a GPS module and an altimeter. GPS is quite useless when it comes to measuring height.
mxk463 wrote:Is there an accurate way to extract the X,Y,Z co-ordinate from a drone?
Tue Dec 02, 2014 2:26 am
Topic: Solar Powered Raspberry Pi A+
Replies: 4
Views: 1470

### Re: Solar Powered Raspberry Pi A+

Have a look at my recent post. It will show you how to calculate the minimum size panel etc. Hello, I'm trying to make my raspberry pi A + model solar powered however I couldn't find many details on voltage or what types of panels/regulators/batteries to use. Has anyone managed to power their pi's v...
Thu Nov 27, 2014 2:22 am
Forum: Troubleshooting
Topic: Relay board connecting to gpio
Replies: 15
Views: 2198

### Re: Relay board connecting to gpio

the link to the relay board shows yet another weird and crazy product without specification. the text talks about a pnp transistor and 5V drive. My guess is that the relay is intended for 5V and uses a pnp transistor as driver. that means that you only can drive it with 5V logic. if you try to drive...