Raspberry Pi Forums

Brandon92

Hi. Thanks for the info. I know about the 5v0 and 3v3 pins, but was not sure about voltage between txd pin and ground. I think also that my LED could still work at a little under 3v0 I will check it. Maybe as I have got various resistors, I could start a little higher and work back towards 60 ohms....

Brandon92

Yes, the cable is rated at maximum 4A. But, this cable has also a resistance of 41R a 304.8 meter. And because you are using a low voltage the resistance is also imported. And I assume that you solder the wires under the usb connector. Is your power supply good, because it should not deliver 5.7V at...

Brandon92

Maybe you problem is in you cable.
When I use a calculation tool for the voltage drop, you will lose around 412mV. If your total wire is 0.5m at 5V and 3A.

edit
I think this is also confirms by the offical power supply for the Rpi. It used a 18AWG cable, and yours is 26AWG (what is smaller).

Brandon92

I think that value is a little bit to big. However you could try it. But I don't think your LED is going to light up.

Lets assume that your led used exact 3V and you tx is exact 3.3V. And you want a current of 5mA trough your led:
R = (3.3-3)/0.005 = 60 Ohm.

Brandon92

I would advice to use a resistor. So, you know that the led doesn't draw to much current. And if you don't use one this could course a problem on your data line.

Brandon92

And are your sure that your total load is less than the maximal current that the power supply can deliver. Because, when the power supply has a over current. It will limit the current and will cause the voltage to drop.

Brandon92

Maybe it's also good idea to post a clear picture of your setup, or a couple. So, we can check if everything is correct. Please check previous post I have posted all connection details Yes, I saw that diagram. But between a theoretical diagram and the real word sometimes a mistake is made. And than...

Brandon92

Maybe it's also good idea to post a clear picture of your setup, or a couple. So, we can check if everything is correct. Also, take a peace of paper. And calculate for your self. So, from input of your current sensor. To the output of the terminal. This will also help you to understand what happends...

Brandon92

Maybe a stupid question, but did you connect the connections to your acs the right way around. If this is not the case, you measure a negative current.

Brandon92

Good that you have found the mistake. And are the values that you are getting what you would expect?

Brandon92

Yup, you are correct. That's why I advised you to use a sensor with a I2C data bus interface. Or does this sensor something that you really need ? DHT22 directly interrupting Rpi, bypassing stupid and slow MCP23017 Well, I actually have bought three other types of sensors to mess around (the most r...

Brandon92

This is the new script. It is all you need. The Voffset is the real offset provide by ACS712-30 then it is 2.5V This script return the Voltage before the resistor divider. it back calculate the real Voltage. https://gist.github.com/danjperron/039e4430d0fa2ff7360c11c9ffab282a This script give follow...

Brandon92

Did you connect the external 5v supply his ground to the ground of your Rpi? Because you didn't draw it in your picture. And can you response to this. So, what for kind of wire are you using for the 4A load: Also, what for kind of wire are you using for the current sensor? I have single core breadbo...

Brandon92

You could change the cameras around. To see if the problem is in your hardware or software.

And is the environment for all the cameras the same?

Brandon92

How did you connect those button and use you a pull-up or pull-down resistor? If you don't that resistor, you input pin is floating. And can have any value. This can trigger constant you interrupt routine.

Brandon92

Good to hear you feedback.

And you can test this out and it should work

Brandon92

Can you post your schematic how you wire everything and possible a picture. And what is the distance between your Rpi and the sensors?
Then we can see what the possible problem is and we don't need to guess what the issue is. However, I have some ideas what could be wrong.

Brandon92

Fan174 wrote: ↑
Fri Sep 14, 2018 6:09 pm

Brandon92 wrote: ↑
Fri Sep 14, 2018 6:02 pm
Also, what for kind of wire are you using for the current sensor?
I have single core breadboard wire

Okay, do you now the diameter of that wire, I assume 0.2mm2?
Or is this type of wire: jumper wires, breadboard wire

Brandon92

Good to hear that you don't try to run it at mains voltage.

Also, what for kind of wire are you using for the current sensor?

Brandon92

Yup, you are correct. That's why I advised you to use a sensor with a I2C data bus interface. Or does this sensor something that you really need?

Brandon92

I think your concern about the reinforced isolation voltage rating is overstated. It is measured from pins to frame, not input to output. The chip package itself will not be the only insulation for the product (it can't be, there are external connections) so there must be an enclosing isolated (or ...

Brandon92

This is not exactly what I meant. This is more my point, the sensor change his output from a 0 to a 1: How long will it take for the MCP to change the inta pin from the time that his input is changed How long does it take before the Rpi know that there is a interupt and start reading the data How lo...

Brandon92

No, that is not correct. You need this ^ schematic for turning on and off your fan.

Brandon92

No really, you need also add a base resistor for the transistor. And add a fly back diode across your fan, for protection.

Brandon92

As propmist my explanation about the safety with the ACP712: To say it a bit bluntly: At the beginning of the topic I expected that you would use this to measure the mains current, and were we are ;) . And to give you some (background) information, why you should not use this sensor. In this topic I...

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