Uno + shield + 1x9V

First of all, please excuse my ignorance, I'm very new to this and trying to resolve that!

I have an Uno with an Adafruit prototype shield.

My plan is to put a 5V regulator on the proto shield to feed into a MAX232 and then feed the resultant signal to an ultrasonic sensor.

I want to power the whole thing via battery.

I was planning on attaching 9V directly to the regulator to output 5V directly into the MAX232, and I need the Uno to control the ultrasonic pulses.

Would the 9V battery be enough to power everything? Also if I attach the battery to the prototype shield, and send the 5V and GND to the corresponding rails or ports on the edges of the shield, will that be enough to feed the Uno?

I hope this makes sense. Many thanks for deciphering.

Would the 9V battery be enough to power everything?

Probably yes, at least for a few minutes. What did you expect? Why can I not find links to the exact hardware you're planning to use? Why do you want to add an additional regulator if the UNO already contains one?

Thanks for your reply.

I don't know what to expect exactly.

Apologies for the missing links.

Adafruit prototype shield

MAX232 datasheet

Planning to use an LM7805C for my own regulator.

I'd like to make sure that 5V goes into my MAX232 so that's why I want to use a regulator coming off the 9V battery. I am hoping that the 232 will then give me around 20 Vpp.

Hi,
Welcome to the forum.

I think we need a bit more explanation about your project.

What are you doing with the MAX232 and to what Ultrasonic sensor?
What is the aim of your project?

Thanks.. Tom... :slight_smile:

pylon:
Why do you want to add an additional regulator if the UNO already contains one?

Because he wants to power something other than the ATmega328 chip and knows that the on-board regulator is not capable of powering anything else but that chip alone?

Smarter than many of the questions here about power supplies. :grinning:

Need a switchmode regulator, and at the minimum, a battery of six alkaline "AA" cells in a carrier.

Because he wants to power something other than the ATmega328 chip and knows that the on-board regulator is not capable of powering anything else but that chip alone?

Bullshit. The UNO’s onboard regulator provides about 500mA of which the onboard components need less then 70mA. So there’s plenty of room to driver other components. I agree that a DC/DC converter is more appropriate for a battery driven project but an extra LM7805 is not needed for the specified hardware.

pylon:
Bullshit. The UNO's onboard regulator provides about 500mA of which the onboard components need less then 70mA. So there's plenty of room to driver other components. I agree that a DC/DC converter is more appropriate for a battery driven project but an extra LM7805 is not needed for the specified hardware.

500mA if it was heatsinked.
There have been many noobs who have problems with using the onboard 5V reg to power even 100mA of peripherals due to regulator power dissipation problems causing the reg to thermally shutdown.
Remember, if you are using the USB port for 5V, the onboard regulator is not being used, so a different current supply characteristic.
Tom... :slight_smile:

There have been many noobs who have problems with using the onboard 5V reg to power even 100mA of peripherals due to regulator power dissipation problems causing the reg to thermally shutdown.

I would bet that these noobs don't use an original Arduino UNO but just any board the cheap Chinese also wrote UNO on.
I have projects that run constantly and draw about 220mA on an Arduino UNO using the onboard voltage regulator and I never saw a thermal shutdown. That gives a bit less than 0.5W (I use 7.5V input voltage) thermal energy to dissipate which didn't pose a problem yet.
The MAX232 draws about 8mA, OP didn't specify yet what ultrasonic sensor is used, so the know components won't be a problem if powered by the internal voltage regulator even if you live in the Sahara.

pylon:
I would bet that these noobs don't use an original Arduino UNO but just any board the cheap Chinese also wrote UNO on.
I have projects that run constantly and draw about 220mA on an Arduino UNO using the onboard voltage regulator and I never saw a thermal shutdown. That gives a bit less than 0.5W (I use 7.5V input voltage) thermal energy to dissipate which didn't pose a problem yet.
The MAX232 draws about 8mA, OP didn't specify yet what ultrasonic sensor is used, so the know components won't be a problem if powered by the internal voltage regulator even if you live in the Sahara.

Exactly, but noobs use 12V supply because its convenient and the UNO specs say up to 12V recommended and 20V max.
Tom... :slight_smile:

The RS232 voltages you mention (+/- 20V) are peak, more often (+/- 12V) - but in reality, almost anything from the last 20 years is happy with +/- 5V excursions.

The MAX232 uses six capacitors as a charge-pump to generate 'compliant' RS232 +/- voltage levels from a single +V supply, and YES, if you're only powering the Arduino and MAX232 from the board - you can use the onboard 5V from the Arduino.
In the datasheet - the MAX232 only draws 10mA maximum - so you're well within the Arduino 'extra' capacity.

If you're adding extra hardware that is powered from the Arduino - then you might need to explore additional power supply options.

lastchancename:
In the datasheet - the MAX232 only draws 10mA maximum - so you're well within the Arduino 'extra' capacity.

Really? Then how (noting it is a "boost" converter) can it deliver a maximum of 10 mA plus or minus to short-circuited outputs?

What you have read, is its quiescent current draw - with nothing else connected, nominal 8 mA up to 10 mA.

Exactly

Hi,

Many thanks for all of your replies, I understood a decent chunk of the discussion so that's a start.

I'm using a 48kHz transceiver to transmit the signal and one to receive.

lastchancename, thank you for your reply about the voltages.

As long as I'm understanding correctly, if I want my ultrasonic signal to travel further, I need to give it more of a 'push' to overcome attenuation. I would like to be able to manipulate the receiver from around 2 metres potentially, which is why I was thinking the MAX232 acting as a kind of voltage doubler would help out. But as I want to also use the Uno to program the length and duration of the pulses, I wanted to also feed that 5V into the Uno as long as it's possible. I thought that if I had a good voltage on the output then I potentially have the ability to increase the initial distance of ≈ 2 metres. I hope that makes sense, sorry if not. I will try to clarify anything.

TomGeorge, do you think I should attach a heatsink to the LM7805 (assuming I should use it at all)? I did wonder about heat as surely that is how the extra voltage is dissipated for want of a better word and I would ideally like to enclose the circuit to protect it, so heat management has occured to me but it sounds like I do need to be active about it.

Sorry if there are other things here that I've not addressed, I'll have another quick run through the replies now.

The signalling voltages used by the MAX232 are just that...signals, they have no bearing on the power supplied to or used by the device at the other end of the wire - than being ‘standards compliant’.
This is why most RS232 devices nowadays are happy with 5V signalling, although the RS232 ‘standard’ says the signal wires should be able to handle up to 20V.

I’d suggest that before going much further, you should sketch out a block diagram of your entire project, so you (and us) can see what’s connected to what.
Don’t leave anything out because it’s not important... it is.

Ah OK I see, I'll review my project and hopefully produce something that is readable/makes sense.

Thanks for taking the time to help me out with this one.

Hello all,

I just thought I'd update anyone interested in this project.

The 9V battery is powering both the Uno and the MAX232 which is driving the ultrasonic transmitter. The voltage inverter on the 232 is working, but I'm having trouble getting the voltage doubler to hit its potential of +10/-10V. I am getting around +7/-6V on the output. I'm about to do some research on why this might be.

Thanks.

edit: I have come to realise that the output is this way because +10/-10V would be an ideal, unloaded situation. The drop in V is due to the attachment of the sensor.

Thanks for everyone's help with this.

plembryo:
I have come to realise that the output is this way because +10/-10V would be an ideal, unloaded situation. The drop in V is due to the attachment of the sensor.

Correct. And for the same reason, the current drawn by the MAX232 will be more than twice what is drawn by the output device.