Reverse Polarity protection
J^3
Posts: 121
Good evening· all,
··· Does any one know a cheap and easy way of protecting against reverse polarity?· Is it as simple as putting a diode in series with the incoming circiut, and if so how do you select the diode?
··· Does any one know a cheap and easy way of protecting against reverse polarity?· Is it as simple as putting a diode in series with the incoming circiut, and if so how do you select the diode?
Comments
You choose a diode based on the amount of current it has to carry and the highest reverse voltage it has to withstand. For high currents or situations where power loss is important, the type of the diode may be important. Ordinary power diodes have a voltage drop across them of about 0.6V. Schottky diodes have a special construction that reduces the voltage drop to about 0.3V, but they're more expensive to make, have a little more reverse leakage, and a lower reverse voltage capability than ordinary diodes.
A common power diode is the 1N4001-4007 series. They all can carry 1A of current continuously and have reverse voltage ratings of 50V, 100V, 200V, 400V, 600V, 800V, and 1000V respectively. RadioShack normally carries the 1N4001-4004 diodes.
I prefer wiring the diode in series with the input supply in the non-ground (usually positive) lead. In that case, the anode goes toward the positive input supply.
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Chris Savage
Parallax Tech Support
This video explains it very well
He has a number of other tutorial videos
https://www.youtube.com/watch?v=IrB-FPcv1Dc
I don't know if the BS-2 can withstand reverse polarity for long. Maybe Chris Savage will reply. He knows these things.
-Phil
Some devices shield the battery contacts with a piece of plastic with holes that won't allow the larger terminal to fit through. This prevents both terminals from making contact when the battery is reversed. This method is commonly used in smoke detectors.
A series diode will also work, but you won't get as many amp-hours out of the battery as you could without the diode. Assuming the board uses a 7805 regulator you will need to replace the battery when it drops down to 7.7 volts instead of 7 volts.
Since the BASIC Stamp 2 module does not have 9V battery terminals there must be a development board that the module is plugged into. Which board are you using? Different boards supply power to the BASIC Stamp in different ways.
Have you read all of this thread? People want to know what carrier board you're using for your BS2. It will help to solve your problem if we knew!
-Phil
I can't seem to get the bluetooth module to work so I think I am going back to the wired connection now. I tried hooking GND to GND, Vin to VDD, and RX and TX to Sout and Sin respectively. Before I did that I tried hooking RST to Stamp PIN 0,Rx to Stamp Pin 1, TX to Stamp Pin 2 RTS to Stamp Pin 3 and CTS to Stamp Pin 4 as it seemed to indicate in the sample software comments (not certain if they are referring to the Stamp or the RN-42 Bluetooth module pins).
I see the device on my computer, I get a blinking green lite and when I run the sample program debug I get the solid green and blue lite and then a warning on my computer that No Stamp Can be found. I just don't get it.
If you are trying to get the Bluetooth module to run from the Stamp's 5V then forget it, its capabilities are modest.
Likewise from a "9V" battery - No Sale.
PE -
Your peripherals' demands (for current) are likely forcing the Stamp into brown-out.
By the way, your schematic doesn't seem to match what's on the breadboard, unless I am missing something. I don't see the Bluetooth Module on the schematic, and you appear to have an external regulator in the schematic that I do not see on the breadboard.
Most everyone has installed a 9VDC battery in a smoke alarm or something similar and tried fitting the battery in place and found that the two fat ends don’t mate no matter how long or hard they push the ends together, then they reverse the battery to its correct designed installation and then all is well. But in that moment of reverse polarity, the electronics are normally protected against momentary inadvertent battery installations. This protection feature would seem to be a key design feature in a learning device such as the Basic Stamp. I have seen some devices with a plastic battery carrier that will only allow the battery to go in one way so there is no chance of reverse polarity issues.
I am using the Basic Stamp 2 Module #BS2-IC-RT with a universal solderless breadboard (just the Basic Stamp 2 carrier board). I am not using something like the Stamp Homework Board. It would seem the answer to this question is a certain yes or no based simply on the board or chip design. If it is not a certain yes answer, then I need protection.
I currently have a Zener diode in series with the battery "+" terminal but I am not happy about the extra space required or the voltage drop with the Zener requires (with the voltage drop, the battery will have to be replaced earlier than needed as well).I have a NTE139A (ZD-9.1 V, 1W) Zener.
Sorry about the confusion in my earlier post. Please feel free to delete my earlier (locked) post as it seems to have caused more confusion than helped.
Also I have answered your question about the reverse polarity in the following duplicate thread: http://forums.parallax.com/showthread.php/157737-Reverse-Polarity-Protection-From-A-9V-Battery?p=1297804&viewfull=1#post1297804
The original BASIC Stamp uses an LM2936 5 volt regulator, which features reverse battery protection. Here from its data sheet with that outlined in red. Note also that it's available output current is only 50mA, which relates to your other question.
Of course, you can't apply 9V forward or reverse to other pins on the Stamp, just Vin, pin 24 on the module. With regard to PJ Allen's response above, "A zener diode is not the thing for "overvoltage protection", a rectifier diode is better suited to that task." Did you read and understand that?