Safety for the DMD Display circuit

The Dot Matrix Display (DMD) is a 32x16 array of high-brightness LEDs for visually striking effects. [Product Page]
Post Reply
statbat
Posts: 44
Joined: Tue Dec 22, 2015 10:53 am

Safety for the DMD Display circuit

Post by statbat » Fri Jun 03, 2016 10:52 am

Hello,

I have made a DMD display circuit with arduino mega.
I am a newbie and all I learned is on this forum. I want to make my circuit secure for any short circuits or any other reason.

Due to any fault, the connection with battery should be automatically broken/disconnected.

Can you guys please advise me what you do to secure your circuits to meet standards

Please advise.
:)

Brissieboy
Posts: 181
Joined: Fri Sep 20, 2013 7:25 am

Re: Safety for the DMD Display circuit

Post by Brissieboy » Sat Jun 04, 2016 2:02 am

statbat,
A fuse is the obvious answer, but one of the certainties with electronics is that the critical components fail MUCH faster than a fuse blows.
While a fuse may not protect the electronics, it should prevent things going up in smoke or burning the house down. A fuse is there to protect the power circuitry from possible overload caused by some form of failure, not really to protect the electronics.
A reverse biased diode (a decent sized one) across the power rails after the fuse may also help prevent damage to the circuitry in the case of the power supply being connected backwards - it will cause the fuse to blow.
A DMD requires quite a bit of current, depending on how many LEDs are on. It can be over 2 Amps.
The Arduino draws very little current in comparison to a DMD - around 50mA from memory.
A fuse should be rated slightly higher than the maximum current your circuit can draw.
I would suggest 3 Amps for a single DMD, but that could be reduced depending on the maximum number of LEDs that your sketch can possibly turn on at the same time.

statbat
Posts: 44
Joined: Tue Dec 22, 2015 10:53 am

Re: Safety for the DMD Display circuit

Post by statbat » Sat Jun 04, 2016 3:23 am

Brissieboy wrote:statbat,
A fuse is the obvious answer, but one of the certainties with electronics is that the critical components fail MUCH faster than a fuse blows.
While a fuse may not protect the electronics, it should prevent things going up in smoke or burning the house down. A fuse is there to protect the power circuitry from possible overload caused by some form of failure, not really to protect the electronics.
A reverse biased diode (a decent sized one) across the power rails after the fuse may also help prevent damage to the circuitry in the case of the power supply being connected backwards - it will cause the fuse to blow.
A DMD requires quite a bit of current, depending on how many LEDs are on. It can be over 2 Amps.
The Arduino draws very little current in comparison to a DMD - around 50mA from memory.
A fuse should be rated slightly higher than the maximum current your circuit can draw.
I would suggest 3 Amps for a single DMD, but that could be reduced depending on the maximum number of LEDs that your sketch can possibly turn on at the same time.
Thanks for a great reply. I will visit JayCar right now. I want some protection. I dont want to burn the house down if i connect battery wrong due to too many drinks the night before :D

statbat
Posts: 44
Joined: Tue Dec 22, 2015 10:53 am

Re: Safety for the DMD Display circuit

Post by statbat » Sat Jun 04, 2016 5:48 am

Brissieboy wrote:statbat,
A fuse is the obvious answer, but one of the certainties with electronics is that the critical components fail MUCH faster than a fuse blows.
While a fuse may not protect the electronics, it should prevent things going up in smoke or burning the house down. A fuse is there to protect the power circuitry from possible overload caused by some form of failure, not really to protect the electronics.
A reverse biased diode (a decent sized one) across the power rails after the fuse may also help prevent damage to the circuitry in the case of the power supply being connected backwards - it will cause the fuse to blow.
A DMD requires quite a bit of current, depending on how many LEDs are on. It can be over 2 Amps.
The Arduino draws very little current in comparison to a DMD - around 50mA from memory.
A fuse should be rated slightly higher than the maximum current your circuit can draw.
I would suggest 3 Amps for a single DMD, but that could be reduced depending on the maximum number of LEDs that your sketch can possibly turn on at the same time.
I have bought and installed this 50VDC 5AMP circuit breaker advised by the guy at shop on the positive wire of my connection.
http://www.jaycar.com.au/Passive-Compon ... r/p/SF2254

For the polarity protection I have put the P-Channel mosfet again bought from Jaycar. P-channel mosfet is working good, i checked it by plugging terminal in opposite.
Brissieboy wrote: across the power rails after the fuse may also help prevent damage to the circuitry in the case of the power supply being connected backwards - it will cause the fuse to blow.
After putting all the connections, soldering everything, after that i noticed this line in your reply. You wanted polarity protection after fuse. I did opposite. First is the P-Channel mosfet, then the breaker, then my entire circuit. Will it be ok ? :(

Brissieboy
Posts: 181
Joined: Fri Sep 20, 2013 7:25 am

Re: Safety for the DMD Display circuit

Post by Brissieboy » Sun Jun 05, 2016 3:34 am

statbat,
That will depend on how you have set up the MOSFET circuitry. If it is as a switch in series with the power supply then you have double-barrel protection to some extent; if it is as crowbar protection (across the power rails) then definitely NOT good.
And circuit breakers are generally much slower than a fuse, and much more expensive. Why not a simple fuse? And 8 Amps?
It is very difficult to provide assistance when you do not give full details. Posting a copy of your circuit would help greatly.

statbat
Posts: 44
Joined: Tue Dec 22, 2015 10:53 am

Re: Safety for the DMD Display circuit

Post by statbat » Mon Jun 06, 2016 10:27 am

Brissieboy wrote:statbat,
That will depend on how you have set up the MOSFET circuitry. If it is as a switch in series with the power supply then you have double-barrel protection to some extent; if it is as crowbar protection (across the power rails) then definitely NOT good.
It is in the series. I will make a diagram and send. I have never made a diagram before. Please mind it :)
Brissieboy wrote: And circuit breakers are generally much slower than a fuse, and much more expensive. Why not a simple fuse? And 8 Amps?
It is very difficult to provide assistance when you do not give full details. Posting a copy of your circuit would help greatly.
The sales man was good. he upsell me the breaker. :?

Post Reply