On the protection subject, In case something would happen in my project being most of it is 12 volt, would a Zener diode to ground on the divider pins be something good to do in case any of the voltages would happen to go high for some reason? The dividers I used give 3.1 volts at 13 volt supply. If one was to open up or something the voltage could go up. A loose ground or something like that. There's about 6 digital and four analog inputs that are 12 volt.
Is it ok if I keep it until I get the new one? Quite a few wires and would like to swap instead of pulling them all off. I hav them diagramed but might make another mistake.
Is it ok if I keep it until I get the new one? Quite a few wires and would like to swap instead of pulling them all off. I hav them diagramed but might make another mistake.
I don't think there's any rush to get it sent back. Maybe when we get it we can try replacing the chip. Then we can use the board in Parallax for something.
Is it ok if I keep it until I get the new one? Quite a few wires and would like to swap instead of pulling them all off. I hav them diagramed but might make another mistake.
I don't think there's any rush to get it sent back. Maybe when we get it we can try replacing the chip. Then we can use the board in Parallax for something.
+5000
That's a lot of jumper cables CRST1 !!!.... I wouldn't think you should rush to remove any of those until you've got the new board wired up and working.
Nice little grey holder, BTW. Did you 3D print that ?
Maybe we should have a optocoupler-isolator , Level translator Prop 2 ES board available . Also , having the screw type terminals for automotive work would be handy.
That's not a bad idea. An industrial IO board was considered a while back, along with a buffered LED breakout that would add signal LED's to any IO. I think they would help CNC/Motor developers too.
I'm sure the breakouts will be revisited as Rev-C chips arrive, and I've pasted your support to the list of ideas for those. Thank you for thinking about these things.
Opto-isolators are the way to go. However, if you want a simpler and cheaper protection, you can get away with a series resistor for each pin, and a TVS diode from each pin to ground. The diode should be rated for 3.3V, and works like a Zener diode (and it is one, albeit faster).
Resistor might be good enough... The pins have Zener diodes built in (I'm pretty sure)…
But, TVS, then resistor, then Prop pin would be extra safe...
The TVS should be right next to the pin. The resistor will limit inrush current resulting from a voltage spike, thus protecting the TVS and the pin. Although the pins have Zener diodes built in, they might not be enough to absorb high energy.
Dual Schottky diodes to ground and 3.3 is the way to go if you really want to protect it. As long as current is limited which it is with the divider, the diodes will clamp to +300mV of supply and- 300mV to ground and they are fast.
Dual Schottky diodes to ground and 3.3 is the way to go if you really want to protect it. As long as current is limited which it is with the divider, the diodes will clamp to +300mV of supply and- 300mV to ground and they are fast.
It might still be necessary to put a zener from that local power supply to ground, to inhibit high voltages from developing on the VIO pin.
Dual Schottky diodes to ground and 3.3 is the way to go if you really want to protect it. As long as current is limited which it is with the divider, the diodes will clamp to +300mV of supply and- 300mV to ground and they are fast.
It might still be necessary to put a zener from that local power supply to ground, to inhibit high voltages from developing on the VIO pin.
If current is limited then there isn't a problem but I have put clamp diodes on my supply as well when I have been using 1K resistors directly into P1 inputs since P1 would draw very little current when reset was low and that would disrupt booting. However I can't really see any problem with the P2 and larger value dividers.
btw, I was going to make a small mention when I posted but I was on my phone and even with swyping I can't be bothered typing too much
btw - for those of you who think zeners are good clamps, just remember that the low voltage ones have a soft knee, they start conducting a bit way before the zener voltage, plus they are slow.
Your solution would redirect any excess voltage to the supply. Not good, IMO, unless you have TVS diodes in the supply (not just any clamps). I rather prefer a more direct approach: it involves killing voltage transients right then and there, instead of letting those being aggravated by track and wire impedance.
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btw - for those of you who think zeners are good clamps, just remember that the low voltage ones have a soft knee, they start conducting a bit way before the zener voltage, plus they are slow.
...
Zener diodes are slow and some of them may have "soft knees". However, I suggested the use of TVS diodes, which are a completely different animal.
I have used LEDs as low-voltage zeners, red for 1.6V at low-current, amber around 1.7V, green around 1.8V and blue varies.
@samuell - "excess current" is in the region of microamps or at worst, a few milliamps, and that is only when the input voltage exceeds the range of the divider and even then how long is that for???????? Rather than "might" mongering, show reasonable proof that this could ever ever be the case.
I have designed countless scores of industrial products and my stuff can even take complete and utter stuff-ups by the installer in its stride, like 240VAC to signal inputs as long as I rate the resistors accordingly.
Here is a quick rule of thumb calculation:
With a divider of around 26k source resistance and 10k sink for 12V-->3.3V it would take about 30V to inject 1ma into the supply which unless it is completely disconnected from the P2 and other loads will have practically zero effect. The sink resistance is not taken into account when it is clamping just to simplify the calculation but it would still be loading the clamped signal by around 260ua assuming clamp voltage = 3.6V.
Nonetheless, I have used a simple clamp diode on supplies but that is mainly because the input resistors were much lower values without dividers and fault currents could be higher. Hardly the case with a mere 12V and reasonably high value divider resistors for relatively low-speed signals.
Nice little grey holder, BTW. Did you 3D print that ?
Yeh it was just a quick design and print so I could put it under the console in the mustang. I make parts for the guy that makes the DeltaMaker printer so he prints things for me when I need them. We're working on printing my new console for my 66 mustang.
@"Peter Jakacki" Many new TVS diode arrays are now being designed so that any excess voltage is not dumped to a supply rail. Namely, those used to protect USB or HDMI data lines. An example of such is the TPD2E2U06.
I'm not worried about "mights". My only advice is to kill any surges right then and there. Of course, a single clamp solution that involves dumping to a supply is always cheaper but, for the reasons stated above, it is hardly better. My opinion, and value as it is.
I don't think there's any rush to get it sent back. Maybe when we get it we can try replacing the chip. Then we can use the board in Parallax for something.
Thanks for the board again. Got it back in and can use the vehicle again.
I will send the other board back to you this week.
Comments
On the protection subject, In case something would happen in my project being most of it is 12 volt, would a Zener diode to ground on the divider pins be something good to do in case any of the voltages would happen to go high for some reason? The dividers I used give 3.1 volts at 13 volt supply. If one was to open up or something the voltage could go up. A loose ground or something like that. There's about 6 digital and four analog inputs that are 12 volt.
I don't think there's any rush to get it sent back. Maybe when we get it we can try replacing the chip. Then we can use the board in Parallax for something.
+5000
That's a lot of jumper cables CRST1 !!!.... I wouldn't think you should rush to remove any of those until you've got the new board wired up and working.
Nice little grey holder, BTW. Did you 3D print that ?
Maybe we should have a optocoupler-isolator , Level translator Prop 2 ES board available . Also , having the screw type terminals for automotive work would be handy.
http://www.icstation.com/images/big/products/8029_7_3091.jpg
http://www.icstation.com/4bit-optocoupler-isolator-level-voltage-converter-board-signal-output-p-8029.html
I'm sure the breakouts will be revisited as Rev-C chips arrive, and I've pasted your support to the list of ideas for those. Thank you for thinking about these things.
Kind regards, Samuel Lourenço
But, TVS, then resistor, then Prop pin would be extra safe...
Kind regards, Samuel Lourenço
It might still be necessary to put a zener from that local power supply to ground, to inhibit high voltages from developing on the VIO pin.
If current is limited then there isn't a problem but I have put clamp diodes on my supply as well when I have been using 1K resistors directly into P1 inputs since P1 would draw very little current when reset was low and that would disrupt booting. However I can't really see any problem with the P2 and larger value dividers.
btw, I was going to make a small mention when I posted but I was on my phone and even with swyping I can't be bothered typing too much
btw - for those of you who think zeners are good clamps, just remember that the low voltage ones have a soft knee, they start conducting a bit way before the zener voltage, plus they are slow.
Your solution would redirect any excess voltage to the supply. Not good, IMO, unless you have TVS diodes in the supply (not just any clamps). I rather prefer a more direct approach: it involves killing voltage transients right then and there, instead of letting those being aggravated by track and wire impedance.
Zener diodes are slow and some of them may have "soft knees". However, I suggested the use of TVS diodes, which are a completely different animal.
Kind regards, Samuel Lourenço
@samuell - "excess current" is in the region of microamps or at worst, a few milliamps, and that is only when the input voltage exceeds the range of the divider and even then how long is that for???????? Rather than "might" mongering, show reasonable proof that this could ever ever be the case.
I have designed countless scores of industrial products and my stuff can even take complete and utter stuff-ups by the installer in its stride, like 240VAC to signal inputs as long as I rate the resistors accordingly.
Here is a quick rule of thumb calculation:
With a divider of around 26k source resistance and 10k sink for 12V-->3.3V it would take about 30V to inject 1ma into the supply which unless it is completely disconnected from the P2 and other loads will have practically zero effect. The sink resistance is not taken into account when it is clamping just to simplify the calculation but it would still be loading the clamped signal by around 260ua assuming clamp voltage = 3.6V.
Nonetheless, I have used a simple clamp diode on supplies but that is mainly because the input resistors were much lower values without dividers and fault currents could be higher. Hardly the case with a mere 12V and reasonably high value divider resistors for relatively low-speed signals.
Yeh it was just a quick design and print so I could put it under the console in the mustang. I make parts for the guy that makes the DeltaMaker printer so he prints things for me when I need them. We're working on printing my new console for my 66 mustang.
I'm not worried about "mights". My only advice is to kill any surges right then and there. Of course, a single clamp solution that involves dumping to a supply is always cheaper but, for the reasons stated above, it is hardly better. My opinion, and value as it is.
Kind regards, Samuel Lourenço
Thanks for the board again. Got it back in and can use the vehicle again.
I will send the other board back to you this week.