We are using a 89c52 cpu in a machine and we are having horrible static issues. When the user touches the machine and discharges static to it it resets the machine. We have tried a lot of grounding throughout the machine and still no luck . It only seems to happen when the humidity drops low ( less then 30 percent or so )and the problem ' fixes ' itself when it gets more humid and less static in the air. Any help would be aprrecaited . Is there anything that can be done now ,after the intitial enginerring has been done , to modify this board to help out ?
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How to reduce static in a CPU based ite
- Thread starter balagary
- Start date
Skogsgurra
Electrical
balgary,
It is very well that you want to understand what's going on. And that is a very good beginning. But wanting to understand doesn't solve your problem.
You need to find someone who thinks, eats and breathes ESD and EMI. Such a person has lived with the phenomena so long that she/he has developed not only a sound scientific foundation, but also an intuitive feel for what to do. Such persons are usually 40+ years old. They also have the instrumentation (ESD gun, fast digital scope etc) that is needed.
Such a person is hard to find. It is even harder to verify that it is the right person you have found. One tip: If you hear lots of bragging - dont hire that person. If you get references and they say she/he is good - then hire.
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
It is very well that you want to understand what's going on. And that is a very good beginning. But wanting to understand doesn't solve your problem.
You need to find someone who thinks, eats and breathes ESD and EMI. Such a person has lived with the phenomena so long that she/he has developed not only a sound scientific foundation, but also an intuitive feel for what to do. Such persons are usually 40+ years old. They also have the instrumentation (ESD gun, fast digital scope etc) that is needed.
Such a person is hard to find. It is even harder to verify that it is the right person you have found. One tip: If you hear lots of bragging - dont hire that person. If you get references and they say she/he is good - then hire.
Gunnar Englund
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
There are static guns that let you "dial-a-human" but your sweat shirt method sounds workable.
Yeah you can remove most the controls and try isolating to a single control. Then work a fix on it. That is an excellent method of attack.
While a scope sounds like a good idea they often confuse static problems by adding new ground paths and capacitance.
Keith Cress
Flamin Systems, Inc.-
Yeah you can remove most the controls and try isolating to a single control. Then work a fix on it. That is an excellent method of attack.
While a scope sounds like a good idea they often confuse static problems by adding new ground paths and capacitance.
Keith Cress
Flamin Systems, Inc.-
A cheap version of the static gun is one of those piezo electric gas lighter thingies...
I worked on a system where a dc to dc converter was regularly burning out.
It transpired that static was the problem in causing latchup of an A2D ic.
Fixed that with caps & transzorbs & such.
Then it started blowing up the clock chip instead.
Ho hum.
I worked on a system where a dc to dc converter was regularly burning out.
It transpired that static was the problem in causing latchup of an A2D ic.
Fixed that with caps & transzorbs & such.
Then it started blowing up the clock chip instead.
Ho hum.
Lots of good advice here. For an excellent source of general ESD information, tips and measurement techniques, check out
- Thread starter
- #25
ok cool gas lighter ignition thing ,, like for a gas grill . I'll try that. I have tried a 'stun gun' with nothing at all to help me , I have been told that the stun gun is about 25-35kv but the static discharge from a person is a much higher range....any confirmation here ?
Does any one want to suggest any quick and dirty fixes for this problem that would save us sometime and effort while we are fine tuning the exact components ?
Any part numbers anyone wants to suggest for those
suppression devices ? Or just scan digikey for these ?
Thanks
Does any one want to suggest any quick and dirty fixes for this problem that would save us sometime and effort while we are fine tuning the exact components ?
Any part numbers anyone wants to suggest for those
suppression devices ? Or just scan digikey for these ?
Thanks
Static discharge from a person is generally less than 35 kV. That's limited by coronal discharge from fingertips.
ESD is typically tested to around 8 to 15 kV for air discahrge. A common model is a 150 pF cap discharged through a 1 kOhm reistor. There are also specs for modeling furniture ot object discharge. There, the capacitance can be up to 500 pF or so, with resistance as low as a few ohms.
A good reference I've used is Electrostatic Discharge: Understand, Simulate and Fix ESD Problems by Michel Mardiguian. ISBN 0-932263-27-5
ESD is typically tested to around 8 to 15 kV for air discahrge. A common model is a 150 pF cap discharged through a 1 kOhm reistor. There are also specs for modeling furniture ot object discharge. There, the capacitance can be up to 500 pF or so, with resistance as low as a few ohms.
A good reference I've used is Electrostatic Discharge: Understand, Simulate and Fix ESD Problems by Michel Mardiguian. ISBN 0-932263-27-5
- Thread starter
- #27
The absolute best (in terms of reliability) is to process all digial inputs entering the board through NPN inverter stages with pull up resistor on the collector and inverse diode between base and emitter. For many I/O use a transistor driver array chip with the built in bias resistors and diode. However this inverts your logic. So that can be a problem. Just tack on a CMOS hex inverter.
Its more components but destructive reset static just cant get through this arrangement thanks to essentially back to back diodes to ground. A good ground that is
Its more components but destructive reset static just cant get through this arrangement thanks to essentially back to back diodes to ground. A good ground that is
- Thread starter
- #29
Since at this time we cannot re-engineer the main board , all of our atttempts to fix this problem must be extrernal to the board , so we need to try something most likely at each input itself. So what ever fix we try will be installed on each switch , so an array might not be feasable.
Pick a Transorb that passes a DC voltage just higher than the logic signals you are running from the controls to the board.
Keith Cress
Flamin Systems, Inc.-
Keith Cress
Flamin Systems, Inc.-
Electrostatic discharge (ESD) is the release of stored static electricity that can damage electrical circuitry. Static electricity is often stored in your body, and discharged when you come in contact with an object with a different potential. The ESD wrist strap safely channels this electricity from your body to a proper ground (the chassis).
"When the user touches the machine and discharges static to it it resets the machine."
Try this:
Before touching the machine, user or operator should wear ESD wrist strap. In order to work properly, the wrist strap must make good contact at both ends (with his skin at one end, and with the chassis/grounding point at the other).
Also check the continuity (Cold Test) between isolated points of your system with the body of the machine.
WARNING: The wrist strap is intended for static control only. It will not reduce or increase your risk of receiving an electric shock from electrical equipment. Follow the same precautions you would use without a wrist strap.
"When the user touches the machine and discharges static to it it resets the machine."
Try this:
Before touching the machine, user or operator should wear ESD wrist strap. In order to work properly, the wrist strap must make good contact at both ends (with his skin at one end, and with the chassis/grounding point at the other).
Also check the continuity (Cold Test) between isolated points of your system with the body of the machine.
WARNING: The wrist strap is intended for static control only. It will not reduce or increase your risk of receiving an electric shock from electrical equipment. Follow the same precautions you would use without a wrist strap.
Skogsgurra
Electrical
I doubt if a wrist strap will be used by the kids operating this arcade game type machine?
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
Gunnar Englund
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
- Thread starter
- #33
For the wrist strap testing idea, 2 questions
1. If the user touches the metal control panel and the problem does not occur , were would the next step be ? Would the user go and try and touch something closer to the main pcb ?
2. What are we proving by doing this ? Or maybe disproving is this doesnt work ?
<agreed kids will not wear a wire strap - kids will never do what you want them to do , but if we told them NOT to wear it - they just might do it
)
1. If the user touches the metal control panel and the problem does not occur , were would the next step be ? Would the user go and try and touch something closer to the main pcb ?
2. What are we proving by doing this ? Or maybe disproving is this doesnt work ?
<agreed kids will not wear a wire strap - kids will never do what you want them to do , but if we told them NOT to wear it - they just might do it
)
Skogsgurra
Electrical
Now - that's a brilliant piece of logic - and thinking!
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
Gunnar Englund
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
When I used to go to video arcades some 25 years ago or so, I used to intentionally shuffle across the carpet and shock the machines. There was quite a range of different behaviors that I would see. Some would reset, some put garbage on the screen, and at least once I got a free replay from doing that. I used to try shocking them in different places to see what would happen. I'm sure I'm not the only one that did this. These machines really see a lot of abuse.
"When the user touches the machine and discharges static to it it resets the machine."
The purpose of the using ESD wrist strap is to discharge the static charge into ground directly through grounding point. Your problem resolves if the charge discharges to ground not through the machine. Its all the PATH we give to the charge to be discharged.
The purpose of the using ESD wrist strap is to discharge the static charge into ground directly through grounding point. Your problem resolves if the charge discharges to ground not through the machine. Its all the PATH we give to the charge to be discharged.
090441982... We are talking about an arcade game!
Can you see yourself putting on an ESD wrist strap before adjusting your TV each time??
Of course your solution will work! But it is totally unrealistic.
You can save all the passenger deaths in aviation if you just make sure you never have any planes leave the ground. Not too useful though.
Keith Cress
Flamin Systems, Inc.-
Can you see yourself putting on an ESD wrist strap before adjusting your TV each time??
Of course your solution will work! But it is totally unrealistic.
You can save all the passenger deaths in aviation if you just make sure you never have any planes leave the ground. Not too useful though.
Keith Cress
Flamin Systems, Inc.-
MacGyverS2000
Electrical
Yeah, but imagine the kids in the ol' station wagon trying to get the 747 next to them on the highway to honk their air horns!
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Dan - Owner
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