Arduino Forum

Using Arduino => General Electronics => Topic started by: groundsman on Jun 11, 2018, 08:36 am

Title: voltage drop
Post by: groundsman on Jun 11, 2018, 08:36 am
Hello.
I have just completed my scoreboard project, which consists of 3 units a treble a double and a single. I have used one ardruino uno, 6 sparkfun TPIC6C596 shift registers. The shift registers are all linked together though the 3 units. The power to the arduino is 12 volt from a transformer. My problem is the first unit which is the single is fine but as the chain progresses I am losing voltage so when I get to the treble unit I have lost 2 volts so the lights are not as bright. I thought I would feed each unit with its own power supply from the transformer. this worked the lights brightness and the voltage where all the same. But what happens is the numbers change but are erratic ( the control is though buttons) Any ideas what is wrong and what I can do to cure this problem.
Thanks Eddie.     
Title: Re: voltage drop
Post by: ReverseEMF on Jun 11, 2018, 08:45 am
Please read this, and then update your post:

How to use this Forum (http://"http://forum.arduino.cc/index.php?topic=149015.0")

[fixed the link]
Title: Re: voltage drop
Post by: groundsman on Jun 11, 2018, 09:26 am
I have clicked the link but It will not open.
Eddie.
Title: Re: voltage drop
Post by: ChrisTenone on Jun 11, 2018, 09:42 am
It's at the top of every subforum page, this link should
work:

http://forum.arduino.cc/index.php/topic,148850.0.html (http://forum.arduino.cc/index.php/topic,148850.0.html)

Are the ground wires of all the power supplies and the other components all hooked together?
Title: Re: voltage drop
Post by: falexandru on Jun 11, 2018, 09:47 am
When you open the General section of the General electronics, there is a "topic" called "How to use this forum".

That section lists some reccomandations that increases the value of the experience of using the forum.

Basically, it is about how to fully describe the problem, to post schematics and full description of what somebody intends to do or what was the problem.

It is sometime difficult - from my personal experience in the forum- to find descriptions of some actions. But at least by attempting to use the commands one can ask for assistance in a more precise way. The experienced people here are very kind and supportive, I can tell from my personal experience.    
Title: Re: voltage drop
Post by: groundsman on Jun 11, 2018, 10:12 am
Hi
Eddie.There are 2 ground wires. One is from the buttons and one from the shift registers. They both go to the ardunio and then back to the power supply that feeds the arduino. All the ground wires on the shift registers are linked together.
Eddie
Title: Re: voltage drop
Post by: Shuzz on Jun 11, 2018, 11:19 am
May I suggest that you draw up a schematic and post that together with your code?

Otherwise we'll only be shooting in the dark.

Also, please describe in as much details as possible what you mean by "erratic behaviour" in the numbers.
Title: Re: voltage drop
Post by: srnet on Jun 11, 2018, 11:28 am
Describing and providing a link for the 'units' would be helpful too.
Title: Re: voltage drop
Post by: NoraTheDoggo on Jun 11, 2018, 05:23 pm
As said before there is not much to go in with this topic. I have included a wiring schematic for three shift registers just remember you may need to change the data clock and latch pins based on you code.
Title: Re: voltage drop
Post by: groundsman on Jun 11, 2018, 06:29 pm
Hi I will drew up my schematic drawing and code and post it.
Eddie.
Title: Re: voltage drop
Post by: NoraTheDoggo on Jun 12, 2018, 07:09 pm
Hello.
 My problem is the first unit which is the single is fine but as the chain progresses I am losing voltage so when I get to the treble unit I have lost 2 volts so the lights are not as bright.    
Just a quick troubleshooting idea: are your LEDS are connected to one resistor? If so split them up and use three or four.
Title: Re: voltage drop
Post by: TomGeorge on Jun 13, 2018, 11:37 am
Just a quick troubleshooting idea: are your LEDS are connected to one resistor? If so split them up and use three or four.
An example of how you connect LEDs to TPIC6C596,

Tom.. :)
Title: Re: voltage drop
Post by: groundsman on Jun 13, 2018, 10:45 pm
My leds are in strips and each led has its own resistor. My TPIC6C596 shift registers are produced by sparkfun so they are different to your drawings. If you look on there web page you will see what I mean. I followed there drawings.
Title: Re: voltage drop
Post by: TomGeorge on Jun 13, 2018, 11:51 pm
Hi,
Does each display module have its own separate power supply wires directly back to the display power supply?

Don't daisy chain the power wires as this will produce your symptoms.

Does the voltage at the powersupply terminals drop, or just the display modules?

Can you post a diagram of how your power supply is distributed please?

Tom... :)
Title: Re: voltage drop
Post by: groundsman on Jun 14, 2018, 10:01 am
Hi Tom George.

I have attached a drawing and hope you can understand it.
If I take a voltage reading before connecting the to the arduino I get 12.4 volts. when I connect them it comes down to 11.4 volts. Should I connect each shift register with its own power supply?
Eddie.
Title: Re: voltage drop
Post by: ChrisTenone on Jun 14, 2018, 11:50 am
Op's drawing, rotated, cropped, resized and isolated:

Title: Re: voltage drop
Post by: TomGeorge on Jun 14, 2018, 03:26 pm
Hi,
You need to connect your modules in a star configuration to make sure the display gets sufficient supply current.

Tom.. :)
Title: Re: voltage drop
Post by: MarkT on Jun 15, 2018, 12:58 pm
The problem with the erratic response is probably due to signal degradation - as the clock and data
signals move from unit to unit there will be degradation particularly of the clock signal - fast logic signals are
not designed to travel more than a foot or so without some sort of conditioning either at sending end
or receiving end or both.

I would suggest adding 100 ohms in series with the clock signal at receiving end of every cable run, and
using a lower data rate.  If the cable runs are more than a few metres you really need to use a physical
signalling method designed for distance, such as RS485.

Regenerating the clock signal at each stage with a buffer is a very good idea - the data already gets
regenerated by the shift register.