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Everything posted by jheissjr

  1. I have a question I think you guys might be able to help me with. If you have a loop of wire and move a piece ferrous metal in and out of it, the inductance changes. This I know. What I don't know is if the inductance also changes depending on where in the loop the metal is placed. Does the inductance change depending on how close or far the metal is to the edge? Or does it stay the same no matter where in the loop the metal is placed.
  2. I know this post is a little dated so I was thinking the people who have the Maxstream and Aerocomm transmitters might have played around with them by now. Do you have any thoughts on them ?
  3. Yes, the reason I am trying to convert a sine wave into a square wave is so I can feed it into a PIC. In stead of using the ADC and a software algorithm to find the frequency, I thought it would be easier and less CPU demanding to use a square wave input where a pin change interrupt and a timer could be used to find the waves period/frequency. Do you think this is do-able
  4. I was also thinking about AC coupling the signal. So I would feed the sine wave into the +input and hook the -input to ground? If I AC coupled the signal, does my picture look right as to how I am picturing it would work?
  5. I have searched for "zero crossing detector" and all the circuits I see are for AC sine waves that are referenced around a positive supply, a negative supply, and a ground. In my situation, I only have 5v and GND, I do not have -5v. The sine wave I am trying to convert into a square wave is biased at about 2.5v between the 0v and 5v rails . I am still searching, but I have not found a peak detector that works using a single supply. I would think a single supply peak detector exists because I thought they used in RF demodulators or discriminators.
  6. I was wondering if I could borrow your guys' EE expertise. I have a project where I need to turn a sine wave into a square wave like in the picture. The project I have is to determine the roll position of a spinning projectile using thermopiles. My question I was hoping you electrical engineering guys could help me with is my need to get the sine wave's DC level. I was wondering what kind of circuit can do this?
  7. I had not realized a patch antennas size is determined by its dielectric. Now that I think about it, I guess it does make sense. Darn, I thought making the antenna bigger would increase its gain. I should have known something that simple would be too good to be true.
  8. I was wondering what the relationship is between a patch antenna's gain and its physical size is. If I wanted to say double a patch antennas gain (add an additional 3 dB), by how much do you increase its physical size. In other words, to add an additional X dB gain to the antenna, you take the current dimensions of the antenna and multiply them by a factor of Y. My question is how do you find Y given how much additional gain you want. This where the confusion comes in. I know it isn't as simple as doubling the dimensions to double the gain because this is what you do to chance the ant
  9. Thanks for the new link. I had not seen the earlier post. I ordered the 2-axis horizon sensor and I am just waiting for some free time to put it together.
  10. Thanks Mr. RC-Cam. I had not seen that post before. Glad there are still in business.
  11. Does anyone know what is going on with Radiohound. I sent them a money order a few weeks ago for an order and it was returned to me today. Secondly, their site has been down since last week. Thirdly, I don't get any replies to emails from them. Does anyone have any insight?
  12. I was looking at some low cost RF transmitters at Radiotronixs but they have relatively low output power. Would it be possible to simply add a RF amp module, something like this, or are using PA modules more involved than just soldering them in? I am interested in increasing the power to around 1 Watt.
  13. I know some people have obtained both Maxstream and Aerocomm transmitters and I was wondering what your thoughts are on them. Do you prefer either one or find they have similiar performance?
  14. I am trying to weigh the benefits of using Manchester coding and packet repetition and was wondering what your thoughts are considering how much interference is normally encountered out on the flying field. I am trying to decide on the most robust communication given the data rate tradeoff. Send one packet: say 30 frames/sec Send each packet twice (incase first packet has error): 15 frames/sec Send one packet but use Manchester coding: 15 frames/sec Send each packet twice using Manchester codi
  15. Sorry, forgot the source: http://www.radiotronix.com/datasheets/WiFi...%20Wi232DTS.pdf
  16. I was doing some reading today and found this information which is very good at explaining the benefits and drawbacks of 900MHz vs 2.4GHz. 1. Link Budget A typical 802.11x link budget is between 90 and 94 dB. This will give an effective range performance of 300-500 feet outdoors and 50-75 feet indoors. In contrast, the Wi.232DTS module link budget is 114dB at the highest RF data rate (152.34kbit/sec) and 122dB at the lower RF data rate (4.8kbit/sec). For every 6dB of link budget improvement, range is effectively doubled. Using this rule of thumb, a Wi.232DTS solution operating at its m
  17. Two more 1) I may remember reading somewhere that on some receivers the servo signal outputs run at 3 volts instead of 5. I checked my receiver and the servo outputs are infact 5 volts but that may not be true on all receivers. Just kind of curious. 2) Is it possible to run two PIC's off of one crystal. If this is possible, would you just branch the leads of the crystal off to each PIC?
  18. Its hard to see (SMD is so small) but I think on my Futaba receiver circuit board, there is a 100k pull up attached to the RSSI output. Maybe I don't need the additional 470k pull up after all. The reason why I thought adding it would be beneficial is that using it extended the RSSI range from 0-1.5v to 0-2.5v with it attached. I have been trying to read into A/D’s and I think the built in A/D converters on PIC's are of the Sigma-Delta type. The one from Maxim I have above is a Successive Approximation A/D, or SAR. I am still trying to figure it out, but apparently Sigma-Delta A/D’s h
  19. Forgot to ask, what chip is used in your receiver.
  20. I looked into this further and unfortunately I was right about the RSSI not being able to drive low impedance loads. I was wrong though about using a pull down resistor when it should be a pull up resistor. It is a sinker and I have found a 470k pull up works about right. The RF chip used in my Futaba R127 receiver that produces the RSSI output is a TA7761. I definitely agree that 2.5k is a considerably low input resistance for an A/D converter. The only place I can find in the A/D's datasheet that talks about this is on here on pg. 10. Do you think this value I am reading is not it?
  21. Incase anyone is interested here is a picture of where the RSSI output can be found on a Futaba R127 receiver. Question.. For the feedback resistor in a regular inverting opamp configuration (Gain = -Rf/Rin), are there disadvantages to using a high value feedback resistor, somwhere in the range of 1Meg-1.5Meg? I would like have a little gain in the buffer, but to do this I would have to a large value resistor in the feedback.
  22. Here is what I get on the RSSI output of a Futaba receiver: 0.2v : Full Strength Signal (Tx on and right next to the receiver) 2.1v: No signal (Tx off) To simulate the load of an ADC pin, I attached a 2k resistor between the RSSI output and ground. But when I do this, the voltage always remains at zero, even with no signal. This tells me the RSSI output is only capable of driving loads with very high impedance’s on the order of 1M ohm. Have you guys also found this problem. I guess this means I will have to use an opamp buffer between the RSSI output and the ADC input if this is inf
  23. Thanks, I was just trying to get an idea of the resolution I will have using a 12 bit ADC (5/(2^12) = .0012v) compared to MAHI's 10 bit resolution (.003v).
  24. Forgot to ask what did you use for the ADC's voltage reference. I assume it is Vdd which would give a range of 0v to 5v but just wanted to make sure.
  25. Mr. RC-Cam For the MAHI, did you connect the FMA's X and Y outputs directly to the PIC's ADC pins? Did you put in a cap between the ADC pin and ground and/or a resistor in series to form a low pass filter (if so what did you set the cut off point as?)
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