Search found 418 matches

by UhClem
Wed Oct 17, 2018 7:45 am
Forum: SparkFun Product Questions
Topic: Trouble with using LMV358 to bridge headset and teensy
Replies: 3
Views: 182

Re: Trouble with using LMV358 to bridge headset and teensy

It is difficult to tell from what I have found but it is possible that the mic requires a DC bias voltage to operate. The documents mention a resistor (2.2K) in series with a small voltage (2.2V) but it isn't clear if that is needed by the mic or just to detect switch closures.
by UhClem
Thu Aug 30, 2018 11:06 am
Forum: Projects
Topic: Hall Sensor Signal Conditioning
Replies: 9
Views: 254

Re: Hall Sensor Signal Conditioning

The only problem with your circuit is the common mode range of the opamp. Try it out in Spice (LTSpice is what I use) if you don't believe me. You could fix that by increasing the opamp supply voltage except that your particular part can't take much more than 5V. (One minor complication is that the ...
by UhClem
Wed Aug 29, 2018 4:26 pm
Forum: Projects
Topic: Hall Sensor Signal Conditioning
Replies: 9
Views: 254

Re: Hall Sensor Signal Conditioning

Analysis using the traditional concepts of the virtual open and the virtual short: Input current is next to nothing so the inputs to the opamp are open circuits. Feedback assures that V+ = V- just as if they were shorted together. But they aren't, see virtual open. Using the virtual short the curren...
by UhClem
Wed Aug 29, 2018 1:15 pm
Forum: Projects
Topic: Hall Sensor Signal Conditioning
Replies: 9
Views: 254

Re: Hall Sensor Signal Conditioning

Is the solution to put a 10K in series with the '+' input? No. It is already working as expected. Or at least as well as can be expected so close to the limit of the common mode input voltage range. Try applying a test current and watch as the output voltage decreases. The 10K resistor would do not...
by UhClem
Wed Aug 29, 2018 10:50 am
Forum: Projects
Topic: Hall Sensor Signal Conditioning
Replies: 9
Views: 254

Re: Hall Sensor Signal Conditioning

Did you notice the common mode input voltage range for that opamp? With a 5V supply 4V is at the edge of its range. But you have misunderstood the operation of the circuit. An opamp has a huge excess of open loop gain so with negative feedback like you have here, the output voltage will be driven so...
by UhClem
Wed Jul 25, 2018 7:35 pm
Forum: Projects
Topic: Trouble with a Transducer - Trying to switch it off
Replies: 10
Views: 553

Re: Trouble with a Transducer - Trying to switch it off

That image is not nearly as useful as an actual schematic. For example, what is the sensor part number? I looked up the part number shown and that is a 5VDC part. The circuitry inside the sensor will not disconnect from its positive supply just because you removed its ground connection. So it could ...
by UhClem
Fri Jun 15, 2018 1:35 pm
Forum: Projects
Topic: Rocket accelerometer
Replies: 13
Views: 637

Re: Rocket accelerometer

i need to collect the acceleration's DATAs as well, so i must use three axis. the kalman filter will help to detect apogee ( the sensor detect the burnout ) so why would it be wasted? The extra two axis will pick up vibration and not much else. So unless you are trying to measure that, it is a wast...
by UhClem
Thu Jun 07, 2018 7:40 pm
Forum: Projects
Topic: Rocket accelerometer
Replies: 13
Views: 637

Re: Rocket accelerometer

I think you would want both, to more accurately measure the two acceleration regimes. If you use one then scale factor (slope) errors do not matter since you start at zero velocity and end at zero. But if you use one accel under thrust and a different accel near apoge, their scale factor errors mat...
by UhClem
Thu Jun 07, 2018 6:41 pm
Forum: Projects
Topic: Rocket accelerometer
Replies: 13
Views: 637

Re: Rocket accelerometer

@UhClem: Don't you agree that for apogee detection, one would want to use a +/- 2g (or similar) accelerometer? Absolutely not. What you are doing is integrating the acceleration and waiting for the velocity to go from positive to negative. I still have a BlackSky AltAcc2 which uses an ADXL50 accel ...
by UhClem
Thu Jun 07, 2018 10:20 am
Forum: Projects
Topic: Rocket accelerometer
Replies: 13
Views: 637

Re: Rocket accelerometer

If the only purpose is determining apogee, then one axis is all you need.

If the only sensor is the accel then the Kalman filter is wasted.
by UhClem
Wed Sep 27, 2017 8:46 am
Forum: Projects
Topic: MPU9250 schematics
Replies: 1
Views: 308

Re: MPU9250 schematics

falaroce wrote:Our CS# pin is connected directly to VCC, Does the lack of a pullup resistor could be the problem?
No. See Figure 2 in the MPU-9250 data sheet.
by UhClem
Sat May 13, 2017 3:57 am
Forum: MSP Microcontrollers
Topic: The 430F5529 Programming Troubles
Replies: 2
Views: 6096

Re: The 430F5529 Programming Troubles

I am not sure what the problem is but some comments: Why are you bit banging SPI when that chip has multiple SPI hardware ports? Your delay routine will get optimized to nothing. I don't know about your specific compiler but look for something like delay_cycles() for reliable spin delays. Or use a t...
by UhClem
Sun Apr 30, 2017 4:54 pm
Forum: SparkFun Product Questions
Topic: need Bright LEDs visible in daylight
Replies: 3
Views: 510

Re: need Bright LEDs visible in daylight

A quick search at Mouser showed amber T1-3/4 LEDs in stock with up to 21,000mcd output. So I don't know what your trouble is. Unless you want a diffused LED in which case the ratings are lower. You may prefer the diffused LEDs because of their wider viewing angle. I don't have a good handle on conve...
by UhClem
Sun Apr 30, 2017 11:27 am
Forum: SparkFun Product Questions
Topic: need Bright LEDs visible in daylight
Replies: 3
Views: 510

Re: need Bright LEDs visible in daylight

LEDs bright enough to be visible in daylight, at currents less than 20mA, have been around for a couple of decades now. All you need to do is pick one from among the many choices. Use the part sorting features at a vendor like DIgi-Key of Mouser to find what you need. As an example, I used PN SSL-LX...
by UhClem
Thu Mar 02, 2017 6:19 am
Forum: SparkFun Product Questions
Topic: BME280 lacks precision
Replies: 7
Views: 1077

Re: BME280 lacks precision

The altitude reading is off by roughly double ( I'm at 136 meters, and the card logs 300+ meters). I suspect a correction factor needs to be included in the code to correct to sea level. Conversion from pressure to altitude is non-linear and subject to problems. Number one being that it assumes a s...