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MP

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Posts posted by MP

  3. FM impedance antenna matching

    in Projects Q/A

    Posted

    13.8V will not hurt a 2N3866. Mouser has them as their PN 610-2N3866 @ $1.50 each. They are also sold by Futurlec, Digitron, American Semiconductor, Electronic Surplus, Ocean State Electronics, and American Electronic Resource. Searches can easily find thousands with PartMiner, Global Spec., and other IC search engines, but beware since you can easily find them at prices like $4.00. These are also available in a TO5 package.
    Advanced Semiconductor, Inc. still manufactures the 2N3866.
    I think the best price can be found from Mouser electronics.

    Digikey has a lot of stuff, but I would not use them as a standard by any means.

    MP

  4. Pool water level stabelizer

    in Inventive/New Ideas

    Posted

    I see no problem with it. I assume you would use a float type switch? Something like this? http://www.homesecuritystore.com/ezStore123/DTProductZoom.asp?productID=1075
    You know, if you find something on the market that you like, you can go here: http://www.uspto.gov/patft/index.html
    to find all the information regarding the patent on it.

    In regards to metal finishes, most hard finishes will withstand a lot of abuse before corroding or rusting. Anodized rods or chrome plated rods are still conductive. Actually, you can purchase special probes, but they cost much more than a home-made one.
    I like the brain storming part of your project. It is always good to get many ideas out in the open before destroying materials on the workbench. Normally, you will find that there are a lot of ways to proceed. Then it is a matter of preference, and sometimes, cost.

    MP

  5. Pool water level stabelizer

    in Inventive/New Ideas

    Posted

    I'm not sure how you were going to connect a switch, but DC voltage will not hurt anyone in the swimming pool. A good finish on the electrode will allow it to last for a long time. If you connect a float to a switch, you would not need transistors. However, I tend to worry when someone talks about switches and live mains around a swimming pool. If you have mains anywhere near the pool, be sure to use a "Ground Fault Interrupter" circuit. I would certainly make sure the mains are not near the pool water. Switches have a tendency to arc when they are triggered.

    The mercury switch mentioned above is not a bad idea if you do not want to make a circuit. It would certainly be a good low maintenance, low cost solution to take care of this problem while the pool is unattended. Mercury switches usually come as a floating device on the end of an insulated wire cable. When the level of the water changes the angle of the float, the mercury switch inside the float changes state. It either turns the circuit on or off. Still it is something that you would not want in the pool while you are using it.

    MP

  6. Pool water level stabelizer

    in Inventive/New Ideas

    Posted

    A couple of rods in the water will not be a reliable trigger for your circuit. There are two parts to the circuit here. One part is the trigger from the pool water. The other part is the control switch to turn the relay on and off.

    Also, I am not sure where I got this drawing. There is certainly room for improvement. One is the need for a protection diode at the relay.

    MP

  13. circuit design

    in Electronic Projects Design/Ideas

    Posted

    Normally, you would use more current when loaded heavily. I am not following why you think you have a current limiting problem since two out of three of these circuits are working fine. Are you able to take a picture of your project?
    I was thinking the problem might be due to lack of heat sink, poor regulation on the power circuit or something mis-wired on the board. Even with 7 amp capability of the battery, you will only use the amount of current needed by the steppers.

    In the case that your steppers will be using high current: It looks to me like you will need current limiting such as figure 10 in the data sheet for motors which are rated higher than the L298 capability. In this case, your easiest solution would be to find smaller steppers which require less current.

    Again, I am not convinced the problem was due to current overload. A picture would sure help.

    MP

  14. car battery tester

    in Projects Q/A

    Posted

    What would be the point? This one is no different than the voltmeters in the dash of cars. When you suggest that someone scrap their project, you should post the replacement that you are suggesting. Thus, a comparison can be made.

    MP

  15. pnp vs npn?

    in Theory articles

    Posted

    Yeah, but indulis is a lot closer to helping andrie use his mind in the right direction.  (right potential?  ;D )  Both circuits could float, etc.

    andrie: as you can see, it is not so basic. Go to the Electronic Resources forum on this site and download the free transistor theory books posted in the messages. This will help you.

    MP

  16. LED display voltmeter

    in Projects Q/A

    Posted

    Are you building this one?
    http://www.electronics-lab.com/projects/test/007/index.html
    You just need to rectify the input with diodes just like you would with any circuit. Just diodes and a cap for ripple. Then adjust the pot so that it reads correctly.

    MP

  17. circuit design

    in Electronic Projects Design/Ideas

    Posted

    You should use heat sinks on all of your L298 chips. Please refer to the data sheet for information regarding this. They run hot.

    In fact, I was just looking through the data sheet and found that you should not exceed 2 amps unless you use a bridge configuration (figure 7).  You should read it very carefully so that you fully understand all that is required for this chip.
    I have attached the data sheet.

    MP

    L298_Data_Sheet.pdf

  18. circuit design

    in Electronic Projects Design/Ideas

    Posted

    Leaving pin 8 open should not have caused a problem. There must be something else also wrong in the circuit or it is possible something touched a pin that caused a power surge to the chip. Perhaps you had one component that was wrong in this one circuit that was different than in the other two. There are many possibilities, including that the chip just got too hot. You are fortunate to have two other duplicate circuits which are working ok. My only suggestion is to rebuild the circuit, make sure it is the same as the other two which are working correctly, try all three circuits one at a time so that you know they are working ok individually, then connect them together again as a complete unit.

    MP

  19. Knight Rider with Halogen Bulb

    in Electronic Projects Design/Ideas

    Posted

    I have to agree with Windoze,
    I don't like to add power transistors to car circuits. Especially where there will be multiple sets of this circuit.
    The Emergency Response agencies have already figured this all out. They use lots of blinking bright lights. They use relays to make these blink. If you do not want to use a relay that will click and has a short life, use a Solid State Relay for this. There will be longer life and less waste. They will cost you more than a TIP32, but reliability will be built in. I have made several devices over the years that use solid state relays. Some are still used in an Industrial environment for better than 20 years.

    MP

  23. circuit design

    in Electronic Projects Design/Ideas

    Posted

    I would look to see if there is anything different on this circuit than the other two. Perhaps you ran a wire wrong or a component is different. This type of error is the most common.
    Can you post pictures and diagrams? It is hard to guess what might be the problem. Did you heat sink the driver chips? Your L298 might have gotten too hot.

    MP

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