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  1. Hello all, I have decided to set before me a little challenge - to make a simple device (for starters only LED toggling will be enough) which could be controlled by any of the Bluetooth capable smart phones on the market these days. After quite some digging around on the internet a lot of things on the subject became clear to me but at the end, like after any good knowledge hunting, I was left with more questions than I started with. :) That is why I turned to this forum for help. I will be very grateful for any help anyone can offer in answering these questions. And here they are: Is there a Bluetooth profile out there which is supported by all smartphones which are advertised as Bluetooth capable? One would imagine that with Bluetooth SIG with over 12k members and interoperability as one of their main goals keeping an eye over Bluetooth implementation on devices everywhere, a profile supported by all Bluetooth capable smart phones should exist. Is OBEX perhaps such a profile? Well actually, the way I understand it, OBEX is a protocol on which some profiles (FTP, OPP) are based am I right? Supporting this protocol is what makes file transfers possible between mobile phones, right? And since all mobile phones support that, OBEX seems like a promising candidate for a "smart phone universal Profile" does it not? I've noticed, that most Bluetooth modules support multiple profiles. This is promising. If there is no common profile for smart phones, one could just check the 2 or 3 most common ones to see if any of the nearby mobile phones uses them and chose the one which the mobile phone uses. Is this as simple as it sounds? Does it even sound simple? :) Do the Bluetooth modules have to be reflashed to change profile or is it all in one stack? Naturally the most commonly used Bluetooth profiles in smart phones are the ones intended for wireless audio link (HSP,A2DP,...). Would it be possible to use one of those profiles to transfer arbitrary data which would in the end not amount to sound? Could that cause any problems with the Bluetooth SIG or any legal problems? Although until everything stays "in the garage" I guess only the technical problems are to fear if they exist. If the answer to the first question is no than I have one more: Does anyone have an idea how to make a Bluetooth capable device connectable to almost all (if not all) Bluetooth capable smart phones out there? Any advice on which Bluetooth RF modules to look at will also be greatly appreciated. So far this one is looking good: http://www.bluegiga.com/WT12_Class_2_Bluetooth_Module I would like to express my gratitude and thank everyone in advance for any help in answering the questions above. Cheers!
  2. Hello! I am fairly new to DC-DC converters and LTspice and have, logically, stumbled on a problem when designing and simulating my first boost converter. The specifications for the converter are: input voltage ranging from 3-12V, output voltage 17V and output current ranging from 10mA to 1.01A. The chip used is LT1170 (fsw=100kHz). I would first like to ask someone, if he or she could check the results for the component values I calculated: L=1.25mH R1/R2=12.7 and for Co I chose 1000uF (the schematic is attached: Boost.asc). If the results are far off I would greatly appreciate if someone could write the right ones and I will try to figure out how to et them. The second thing I would like to check is, weather it is OK to choose R1 and R2 so that they would also act as a shunt, to always guarantee the minimum 10mA current (for continuous mode). Then there are the initial "bumps" in L current when running the transient analysis. The current rises to 9A in the start and is then somehow limited by something. What is the cause of this high current and how to limit that? Can anyone help me with that please? The problem of the bumps gets even worse when output current is increased (attachment Boost2.asc) because now the output voltage and inductor current start oscillating. I have a feeling, that could be corrected with the proper values of C2 and R4. But my problem is that I do not know what this values are. I read something about how to choose them in LTC application note AN19, but the process for choosing C2 and R4 described there, doesn't work. At least not in the simulation. Are there possibly any known issues with switching regulator IC spice models when simulating in LTspice? Is there something extra that needs to be taken into account when simulating. My next step is to simply buy the elements and test it on protoboard, but the high currents shown in the simulation worry me because I wouldn't like to smoke my room. I would greatly appreciate any help and would like to thank everyone in advance for their answers. Cheers! BoostConv.rar
  3. Thank you for the reply. I've missed the minimum voltage gain 3, but in the simulation the output of the follower outputs a nice square wave (at least in the spice simulation) despite the gain lower than three. Another thing which indicates, that the opamp is not to blame is, that the problem (the curved triangle wave) disappears by only lowering the diodes junction capacitance. After that correction the output triangle is as it should be, with the ne5534s in the circuit. I will however try a different opamp when I get home and see what happens. Does anyone have any recommendations which one to use? As already mentioned, I am fairly new to electronics and do not yet have my own list of favorite opamps. Therefore any opamp candidates for such a list will be very welcome. cheers
  4. Hello! I have been trying to build a generator, which will output a triangle/sawtooth wave with variable frequency and duty cycle. I came up with the circuit attached to the post. It works quite nice up to around 500kHz (my aim is 1Mhz) but then the problems begin. Actually the most disturbing problem is the distortion seen on the attached images. I have traced the problem to the junction capacitance of the two diodes (decreasing the value of this parameter in the simulation reduces the distortion). I've been searching the web for diodes with small junction capacitance, but was unable to find an adequate one (according to the simulation Cj would have to be lower than 300fF - the lowest I could find has 1,5pF). One solution is adding diodes in series and lowering the capacitance that way, but this solution is by no means an elegant one and brings with it other problems (bigger voltage drops->smaller current and frequency, larger variation in the combined voltage drop which is dependent on the current,...). My question therefore is: how to solve this problem? Any ideas for circuit improvement which resolves the problem, or a completely different design which satisfies the mentioned requirements (variable frequency up to 1Mhz, variable duty cycle-preferably from 1% to 99%) would be greatly appreciated. I would however like to avoid the use of OTAs as in this idea: http://www.till.com/articles/VariableSaw/index.html The second problem I encountered presents itself already at frequencies at which the above described problem does not yet cause noticeable distortion. This second problem is the changing of frequency with the change of duty cycle (rotation of potentiometer P2). At 50% duty cycle the frequency is largest. Then at 1% and 99% duty cycle, the frequency drops.For example: at 113kHz with 50% DC, it drops to about 110kHz at 1% and 99% DC. So my second question is: where is the reason for that? When tossing around the equations I came to the conclusion, that the frequency should stay the same for the given circuit. Maybe some parasitic effects are causing the problem again? One reason might be the exponent-like changing of the diodes forward voltage with current, but I also simulated the circuit with ideal diodes and the problem remains. Any ideas? I am fairly new to electronics so I am hoping that the solutions will be quite obvious to some of you more experienced members of the forum and wil therefore not take too much of your time. I thank you in advance for all your answers and help. Cheers, Nejc
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