ATTiny85 with PIR sensor and two LED strips USB connectors  

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Farah Haddad
(@fhaddad)
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2020-02-12 7:55 am  

@casey

Yes the “it” refers to the LED strip 


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Farah Haddad
(@fhaddad)
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2020-02-12 7:57 am  

@casey

The “it” refers to the power supply not the circuit 


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casey
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2020-02-12 7:57 am  
Posted by: @fhaddad
Is all what I said correct ??

Not sure as I couldn't picture what you were suggesting.

However if you connect four 1.2 volt cells in series the mAh value will remain about the same.  In other words the resulting 4.8 volt battery of cells will last same amount of time as each single cell because the extra voltage means extra current drawn.  If you increase the voltage four times you increase the the current four times. So to run the LED strip for more hours use larger electric cells.

You can make the mAh larger by connecting two or more cells in parallel but I don't think that is recommended.  Essentially cells in parallel make the total plate area bigger which is the same as using a bigger cell.

https://www.primaryconnections.org.au/sites/all/modules/primaryconnections/includes/SBR/data/Phy/sub/seriespara/seriespara.htm

 

 


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Robo Pi
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2020-02-12 8:02 am  
Posted by: @fhaddad

@robo-pi

That’s bad you can’t see the video I am just showing how the voltage drops to 3.6V when I connect the LEF strip and yes the LED works fine when I connect them 

It's really difficult to troubleshoot something via posts without being there.   How did you adjust the output of the buck converter?    You may need to adjust the output you want while it is under load.   Sometimes if  you set them for 5 volts with no load and then attach the load the voltage will drop below what you had set it without a load.   So my first guess would be to adjust the voltage of the buck converter with the load attached.

This assumes you don't have any wiring errors! ? 

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James


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casey
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2020-02-12 8:04 am  

Does the current drop when you connect anything else to the power supply?

 

 


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NewburyPi
(@dale)
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2020-02-12 3:47 pm  

Power Supply Question:

I was able to view the video, but only after I down loaded it. What I see is a candle, a big bottle of Kombucha, and a power supply that has gone into current limit. When the current draw rises above a set limit, the voltage will reduce to compensate. That is, there is a load (ohms law tells me it is about 15 ohms), that draws more than 242 mA, and the power supply has dropped it's voltage output to 3.6 volts to accommodate. It is likely that the power supply has been set for 242 mA, and you will have to increase the current limit to something higher (350 mA to 400 mA would likely do.), by adjusting the second knob from the left. 

 

Post Script:

As you are connecting the power supply directly to the LEDs, be careful not to exceed the current specification of the LED when you adjust the power supply's current limit knobs. 

This post was modified 2 months ago by NewburyPi

--
Dale


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NewburyPi
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2020-02-12 4:07 pm  

@fhaddad

Correct, except that there will also be power losses in the buck/boost converter. I would expect about 25% loss in charge capacity (mAh). To follow on your math... you would get closer to 3 hours of operation. You might consider using a buck converter. This type of DC to DC converter tend to be more efficient. 

 

Buck/Boost converters - 70% to 80% efficient

Buck converters - 80% to 95% efficient

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Dale


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NewburyPi
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2020-02-12 4:30 pm  

Sorry to be late to the show, but I believe you have a significant issue with your design. The schematic shows the the LEDs are being driven by the output pins of the ATtiny85. The datasheet (Pate 161) shows that these pins are capable of supplying only 40 mA of current. Far less than the 300 mA that i have seen mentioned above. You will have to insert some sort of MOSFET switch circuit to manage that amount of current.

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Dale


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Robo Pi
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2020-02-12 6:01 pm  
Posted by: @dale

Sorry to be late to the show, but I believe you have a significant issue with your design. The schematic shows the the LEDs are being driven by the output pins of the ATtiny85. The datasheet (Pate 161) shows that these pins are capable of supplying only 40 mA of current. Far less than the 300 mA that i have seen mentioned above. You will have to insert some sort of MOSFET switch circuit to manage that amount of current.

Nice catch Dale!    I should have seen that as well.  Shame on me!

DroneBot Workshop Robotics Engineer
James


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NewburyPi
(@dale)
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2020-02-12 6:33 pm  

@robo-pi

🙂 Some times it's an issue of "forest for the trees." Some times there's road construction too. 

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Dale


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casey
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2020-02-12 8:17 pm  
Posted by: @dale

 The schematic shows the the LEDs are being driven by the output pins of the ATtiny85. 

Yes I was going to mention that and tried to find a suitable MOSFET circuit example on the internet but all the examples appear to be about driving a RGB digital 12 volt LED strip (or 12 volt motor) not the 5 volt analog LED strip. 

I don't have an equivalent LED strip otherwise I would experiment myself on the problem.

One thought I had on a power source might be a 5 volt USB Portable Power Bank like the one I use to power my RPi.  It has a capacity of 10,000mAh and 3Amp max.

 

This post was modified 2 months ago by casey

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NewburyPi
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2020-02-12 9:17 pm  

This may work... I have used a Pololu Buck/Boost converter in in the past (PN-S9V11MA). It has an enable pin. The converter can be turned on and off via this pin. However, the question now is how to manage the constant current to the LEDs. Perhaps current limit is built-in to the LED assembly.

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Dale


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casey
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2020-02-12 9:54 pm  
Posted by: @dale

 Perhaps current limit is built-in to the LED assembly.

If you look at the slide show  here  you can see circuits in the strip.  Click image of computer keys on the left to start the slide show.  I assume the LEDs are connected in parallel with the power source each with a resister to limit the current for each LED.

 

This post was modified 2 months ago by casey

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Farah Haddad
(@fhaddad)
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2020-02-12 10:34 pm  

This is really helpful I will Do the wiring on solder-less breadboard and will post the circuit schematic and let you know the result. I have a MOSFET IRF540N would that work?

CCF46128 26A8 448E 9F73 729BA8F41304

thank you su much really helpful

This post was modified 2 months ago by Farah Haddad

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NewburyPi
(@dale)
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2020-02-12 11:40 pm  

IRF540 looks like a good candidate. More then powerful enough and the max Vgs(th) is 4 volts. As long as you drive the ATting85 on 5 volts, you should be able to drive quite well. 

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Dale


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