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1  Using Arduino / General Electronics / Re: Huge voltage drop from H-bridge (4*N-channel Mosfets) on: July 06, 2014, 02:17:14 pm
Guess I should have done my homework before I started to solder my own H-bridge.

I have ordered some P-channel mosfets now. The FET driver ICs seems really good but they are quite expensive.
While I am waiting for delivery I will use relays.

The bridge is for a solar tracker I have made. A Attiny85 wake up from sleep every 5 minute and read two LDRs, adjust (if needed) a linear actuator for 1 second before it goes to sleep again.
The Attiny85 & LDR part work very well but I need a motor driver.

Relays work but for how long? 12 times every hour * 8760 hours (one year) equals 105120 switches!

 

2  Using Arduino / General Electronics / Re: Huge voltage drop from H-bridge (4*N-channel Mosfets) on: July 06, 2014, 12:54:44 pm
Thanks all!

Now I have some options to think about.

1. Buy P-channel mosfets and rebuild the H-bridge.

2. Use a higher voltage power-supply and step down the voltage to the motors (motor only used 0,4A when I measured).

3. Use 12V and step up the voltage to the gates.

4. Buy a driver IC
3  Using Arduino / General Electronics / Re: Huge voltage drop from H-bridge (4*N-channel Mosfets) on: July 06, 2014, 10:22:28 am
Thanks, for the reply.
I do not have any P-channel mosfets. I will order some from ebay.
Any recommendations? FQP27P06 and irf9530 are cheap.

Is it possible to get my current N-channel H-bridge to work without a driver chip? (Just wondering)
4  Using Arduino / General Electronics / Re: Huge voltage drop from H-bridge (4*N-channel Mosfets) on: July 06, 2014, 10:11:16 am
Hi!

I attach a new schematic. Realy need a better program than mspaint for drawing schematics smiley

I get 7,6V when measuring over the motor.
Q1, Q2, Q3 and Q4 are irf520.

No MCU is connected when testing. I just manually apply a voltage at R1 or R2.
5  Using Arduino / General Electronics / Huge voltage drop from H-bridge (4*N-channel Mosfets) on: July 06, 2014, 08:33:57 am
Hi!

I have made a simple H-bridge with four IRF540. (see attached picture, the symbols are NPN-transistors instead of N-channel mosfets but else everything is the same)

I drive the gates with 12V. Everything works, I can change direction but the voltage to the motor is only ~7V instead of 12V when I measure.

I don't use PWM, only need to swith the motor on/off one second every 5 minute.

Is something wrong with the use of four IRF540 instead of two p-channel mosfets and two n-channel mosfets?
I would like to know if it should work before I continuing to look for bad wiring.
6  Community / Exhibition / Gallery / Re: Water level alarm that uses a pressure sensor, sends SMS on: June 17, 2014, 02:08:43 pm
Hi Bengpaul!

I'm sorry but I have given away the "alarm", it is installed 300km from my home so I can't give you any more details except the code.

/Olof
7  Using Arduino / General Electronics / Re: Measuring AC frequency (48-58V), will this work? on: June 11, 2014, 12:28:22 pm
I already have good code to count frequency. I made the code for my function generator.
Basically I use interrupts and timer1 to count the time between pulses.

If the frequency exceeds 800Hz I change method to "pulses over time" because it works better for higher frequencies.

Back to the topic. Diode + 4N35  or H11AA1. It doesn't  matter both work but the diode + 4N35 generate fewer interrupts.
8  Using Arduino / General Electronics / Re: Measuring AC frequency (48-58V), will this work? on: June 11, 2014, 10:56:22 am
As soon as I get some time off I will test the circuit.
I think I will add a Atmega8, MAX7219 and a 7-seg display to build a very cheap frequency  counter.

I think the frequency should be the same as the wind turbine rpm.  Guess I should not assume things like that when I have no training in electronics smiley

9  Using Arduino / General Electronics / Re: Measuring AC frequency (48-58V), will this work? on: June 11, 2014, 01:21:45 am
So if I wan't to measure the frequency of a variable voltage between 10-58V then I need a 4K resistor.

58V  / 4 = 14,5mA (0.841W) * 0,2 = 2,9mA
10V / 4 = 2,5mA * 0,2 = 0,5mA

Or use less current when measuring. Maybe a 20K resistor will work fine without getting interferences.

I really appreciate the help, thanks.
10  Using Arduino / General Electronics / Re: Measuring AC frequency (48-58V), will this work? on: June 11, 2014, 12:10:28 am
Thanks for the warning.
I just misspelled the component, checked my "component trays" and found ten H11AA1.

What about minimum current to drive the IR-led? More current on IR-led = more current on the transistor base?
 
Looking at picture ih11aa1_06 in the datasheet.
Say I wanted to pull 20mA on the transistor side, should I then (looking at the picture) power the led with 30mA if the temperature is 25 degree?
Do I interpret the datasheet correct?
11  Using Arduino / General Electronics / Re: Measuring AC frequency (48-58V), will this work? on: June 10, 2014, 02:39:07 pm
Thanks for the reply!

I think I have some H1AA1.
So I just use one H1AA1 and a resistor smiley, much easier.

I will use a 10K 0,5W resistor and see how low voltage I can measure the frequency of.

12  Using Arduino / General Electronics / Measuring AC frequency (48-58V), will this work? on: June 10, 2014, 02:02:28 pm
Hi!

I have a question about measuring the frequency of the output of a synchronous generator (3-phase, wind turbine).
The generator is not running yet but I think the voltage will vary between 0-58V (I have a charge controller that regulates the voltage, ~48V when charging batteries and 58V when dump load is active )

My idé is to use one diode as a rectifier and a zener diode to get a regulated voltage. To isolate the MCU I thought a optocoupler would work.
I have never used a optocoupler before and don't know the minimum current to get it working.

I have tried to read the datasheet (http://www.vishay.com/docs/81181/4n35.pdf)  but is not sure what to look for.
Where can I see the minimum voltage requered, is it picture i4n25_06? Then 0,5mA is not enough?

Is the zener diode in my circuit unnecessary? (se attached picture)

Properly you know a much better way to measure the AC frequency!

/Olof
13  Community / Exhibition / Gallery / Re: Water level alarm that uses a pressure sensor, sends SMS on: May 22, 2014, 05:40:31 am
Hi!

The ADC outputs 0-5V.
The sensor outputs 4-20ma and if you use a 250ohm resistor you get an output of 1-5V.
Therefore  1V or 20% of the ADC resolution is "lost". Else I think you got it right.

I have not tried to measure more accurate than 1 cm, It was not important in my project.
Here is a link to the sensor: http://www.holykell.com/en/product/Pressure/Pressure_Transmitters/Level%20Pressure_Transmitters/210.html

You can choose configuration when you order the sensor (pressure range, signal output etc.)

To read 4-20ma with a ADC you can use the attatched circuit. I replaced the 220ohm resistor with 250ohm. I also added a 5.1V zener diod for over voltage protection but that is optional.

14  Community / Exhibition / Gallery / Re: Greenhouse irrigation system on: May 21, 2014, 12:56:00 pm
Two more pictures.
15  Community / Exhibition / Gallery / Greenhouse irrigation system on: May 21, 2014, 12:47:55 pm
Hi!

This is an old project of mine. One of my first projects I made when I started with Arduino for a couple of years ago.
The wiring is a mess but I had no prior experience with electronics then.

I often see questions about watering automation in the project guidance so I decided to show my old project.
It has worked without problem for three years now (four years if I count the first version that did not use solenoid valves).

The system use a  small 12v pump and ten solenoid valves (purchased from ebay).
Only one solenoid is open at a time to  withhold pressure.

I also use two 74HC595 shift registers to control two uln2803 8-channel darlington transistor arrays to drive the valves and the pump relay.

The system also has a thermometer and a home made moisture sensor. The moisture sensor can start the watering schema if the soil get to dry.

It is possible to configure the following in the menu:

Activate/Inactivate valves (each valve can be active or inactive)
Which days and time to water (supports two individual schemas)
How many seconds to water each plant.
Activate/Inactivate moister sensor
Activate/Inactivate schemas (When inactivated watering is started by pressing a button)
Save configuration to eeprom




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