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| author | Keith Packard <keithp@keithp.com> | 2013-01-24 14:30:25 -0800 |
|---|---|---|
| committer | Keith Packard <keithp@keithp.com> | 2013-01-24 14:30:25 -0800 |
| commit | 4692989d1d0b04df591963596088f9c3d04f9f8a (patch) | |
| tree | 3a55e19ed5424fd8ead651763afae64d877c16be /AltOS/doc/micropeak.html | |
| parent | 302a2c83e5a33973e248babb191f30404d0bb025 (diff) | |
Add pre-release version of 1.2 for MicroPeak
Signed-off-by: Keith Packard <keithp@keithp.com>
Diffstat (limited to 'AltOS/doc/micropeak.html')
| -rw-r--r-- | AltOS/doc/micropeak.html | 234 |
1 files changed, 207 insertions, 27 deletions
diff --git a/AltOS/doc/micropeak.html b/AltOS/doc/micropeak.html index cadb1d5..8a0f85c 100644 --- a/AltOS/doc/micropeak.html +++ b/AltOS/doc/micropeak.html @@ -1,4 +1,4 @@ -<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>MicroPeak Owner's Manual</title><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" title="MicroPeak Owner's Manual"><div class="titlepage"><div><div><h1 class="title"><a name="idm14762280"></a>MicroPeak Owner's Manual</h1></div><div><h2 class="subtitle">A peak-recording altimeter for hobby rocketry</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Keith</span> <span class="surname">Packard</span></h3></div></div><div><p class="copyright">Copyright © 2012 Bdale Garbee and Keith Packard</p></div><div><div class="legalnotice" title="Legal Notice"><a name="idp172816"></a><p> +<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>MicroPeak Owner's Manual</title><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" title="MicroPeak Owner's Manual"><div class="titlepage"><div><div><h1 class="title"><a name="idm14841928"></a>MicroPeak Owner's Manual</h1></div><div><h2 class="subtitle">A recording altimeter for hobby rocketry</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Keith</span> <span class="surname">Packard</span></h3></div></div><div><p class="copyright">Copyright © 2012 Bdale Garbee and Keith Packard</p></div><div><div class="legalnotice" title="Legal Notice"><a name="idp108880"></a><p> This document is released under the terms of the <a class="ulink" href="http://creativecommons.org/licenses/by-sa/3.0/" target="_top"> Creative Commons ShareAlike 3.0 @@ -6,7 +6,15 @@ license. </p></div></div><div><div class="revhistory"><table border="1" width="100%" summary="Revision history"><tr><th align="left" valign="top" colspan="2"><b>Revision History</b></th></tr><tr><td align="left">Revision 0.1</td><td align="left">29 October 2012</td></tr><tr><td align="left" colspan="2"> Initial release with preliminary hardware. - </td></tr></table></div></div></div><hr></div><div class="acknowledgements" title="Acknowledgements"><div class="titlepage"><div><div><h2 class="title"><a name="idp174776"></a>Acknowledgements</h2></div></div></div> + </td></tr><tr><td align="left">Revision 1.0</td><td align="left">18 November 2012</td></tr><tr><td align="left" colspan="2"> + Updates for version 1.0 release. + </td></tr><tr><td align="left">Revision 1.1</td><td align="left">12 December 2012</td></tr><tr><td align="left" colspan="2"> + Add comments about EEPROM storage format and programming jig. + </td></tr><tr><td align="left">Revision 1.2</td><td align="left">20 January 2013</td></tr><tr><td align="left" colspan="2"> + Add documentation for the MicroPeak USB adapter board. Note + the switch to a Kalman filter for peak altitude + determination. + </td></tr></table></div></div></div><hr></div><div class="acknowledgements" title="Acknowledgements"><div class="titlepage"><div><div><h2 class="title"><a name="idp772792"></a>Acknowledgements</h2></div></div></div> <p> Thanks to John Lyngdal for suggesting that we build something like this. </p> @@ -21,7 +29,7 @@ Keith Packard, KD7SQG<br> NAR #88757, TRA #12200<br> </p></div><p> </p> - </div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="chapter"><a href="#idp176024">1. Quick Start Guide</a></span></dt><dt><span class="chapter"><a href="#idp1555544">2. Handling Precautions</a></span></dt><dt><span class="chapter"><a href="#idp1561440">3. Technical Information</a></span></dt><dd><dl><dt><span class="section"><a href="#idp3211240">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp1961960">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp2901888">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp1674792">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp1421872">5. Mechanical Considerations</a></span></dt></dl></dd></dl></div><div class="chapter" title="Chapter 1. Quick Start Guide"><div class="titlepage"><div><div><h2 class="title"><a name="idp176024"></a>Chapter 1. Quick Start Guide</h2></div></div></div><p> + </div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="chapter"><a href="#idp774040">1. Quick Start Guide</a></span></dt><dt><span class="chapter"><a href="#idp3062232">2. Handling Precautions</a></span></dt><dt><span class="chapter"><a href="#idp2529968">3. The MicroPeak USB adapter</a></span></dt><dd><dl><dt><span class="section"><a href="#idp2069328">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp1986896">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp3318344">3. Analyzing MicroPeak Data</a></span></dt><dt><span class="section"><a href="#idp785616">4. Configuring the MicroPeak application</a></span></dt></dl></dd><dt><span class="chapter"><a href="#idp3018560">4. Technical Information</a></span></dt><dd><dl><dt><span class="section"><a href="#idp3018880">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp3020504">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp3022056">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp3023856">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp3025920">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp3027624">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp52184">7. MicroPeak Programming Interface</a></span></dt></dl></dd></dl></div><div class="list-of-tables"><p><b>List of Tables</b></p><dl><dt>4.1. <a href="#idp3028936">MicroPeak EEPROM Data Storage</a></dt></dl></div><div class="chapter" title="Chapter 1. Quick Start Guide"><div class="titlepage"><div><div><h2 class="title"><a name="idp774040"></a>Chapter 1. Quick Start Guide</h2></div></div></div><p> MicroPeak is designed to be easy to use. Requiring no external components, flying takes just a few steps </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> @@ -35,7 +43,8 @@ NAR #88757, TRA #12200<br> preparing a soft cushion of wadding inside a vented model payload bay. Wherever you mount it, make sure you protect the barometric sensor from corrosive ejection gasses as those - will damage the sensor. + will damage the sensor, and shield it from light as that can + cause incorrect sensor readings. </p></li><li class="listitem"><p> Turn MicroPeak on. Slide the switch so that the actuator covers the '1' printed on the board. MicroPeak will report @@ -68,11 +77,10 @@ NAR #88757, TRA #12200<br> pressure and blink that value out on the LED. After that, MicroPeak powers down to conserve battery power. </p></li><li class="listitem"><p> - Recover the data. Turn MicroPeak off for a couple of seconds - (to discharge the capacitors) and then back on. MicroPeak + Recover the data. Turn MicroPeak off and then back on. MicroPeak will blink out the maximum height for the last flight. Turn MicroPeak back off to conserve battery power. - </p></li></ul></div></div><div class="chapter" title="Chapter 2. Handling Precautions"><div class="titlepage"><div><div><h2 class="title"><a name="idp1555544"></a>Chapter 2. Handling Precautions</h2></div></div></div><p> + </p></li></ul></div></div><div class="chapter" title="Chapter 2. Handling Precautions"><div class="titlepage"><div><div><h2 class="title"><a name="idp3062232"></a>Chapter 2. Handling Precautions</h2></div></div></div><p> All Altus Metrum products are sophisticated electronic devices. When handled gently and properly installed in an air-frame, they will deliver impressive results. However, as with all electronic @@ -86,14 +94,13 @@ NAR #88757, TRA #12200<br> Thus we recommend that you take some care when handling MicroPeak to keep conductive material from coming in contact with the exposed metal elements. </p><p> - The barometric sensors used in MicroPeak is - sensitive to sunlight. Please consider this when - designing an installation, for example, in an air-frame with a - see-through plastic payload bay. Many model rockets with payload bays - use clear plastic for the payload bay. Replacing these with an opaque - cardboard tube, painting them, or wrapping them with a layer of masking - tape are all reasonable approaches to keep the sensor out of direct - sunlight. + The barometric sensor used in MicroPeak is sensitive to + sunlight. Please consider this when designing an + installation. Many model rockets with payload bays use clear + plastic for the payload bay. Replacing these with an opaque + cardboard tube, painting them, or wrapping them with a layer of + masking tape are all reasonable approaches to keep the sensor + out of direct sunlight. </p><p> The barometric sensor sampling ports must be able to "breathe", both by not being covered by foam or tape or other materials that might @@ -103,7 +110,119 @@ NAR #88757, TRA #12200<br> As with all other rocketry electronics, Altus Metrum altimeters must be protected from exposure to corrosive motor exhaust and ejection charge gasses. - </p></div><div class="chapter" title="Chapter 3. Technical Information"><div class="titlepage"><div><div><h2 class="title"><a name="idp1561440"></a>Chapter 3. Technical Information</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#idp3211240">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp1961960">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp2901888">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp1674792">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp1421872">5. Mechanical Considerations</a></span></dt></dl></div><div class="section" title="1. Barometric Sensor"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3211240"></a>1. Barometric Sensor</h2></div></div></div><p> + </p></div><div class="chapter" title="Chapter 3. The MicroPeak USB adapter"><div class="titlepage"><div><div><h2 class="title"><a name="idp2529968"></a>Chapter 3. The MicroPeak USB adapter</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#idp2069328">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp1986896">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp3318344">3. Analyzing MicroPeak Data</a></span></dt><dt><span class="section"><a href="#idp785616">4. Configuring the MicroPeak application</a></span></dt></dl></div><p> + MicroPeak stores barometric pressure information for the first + 48 seconds of the flight in on-board non-volatile memory. The + contents of this memory can be downloaded to a computer using + the MicroPeak USB adapter. + </p><div class="section" title="1. Installing the MicroPeak software"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp2069328"></a>1. Installing the MicroPeak software</h2></div></div></div><p> + The MicroPeak application runs on Linux, Mac OS X and + Windows. You can download the latest version from + <a class="ulink" href="http://altusmetrum.org/AltOS" target="_top">http://altusmetrum.org/AltOS</a>. + </p><p> + On Mac OS X and Windows, the FTDI USB device driver needs to + be installed. A compatible version of this driver is included + with the MicroPeak application, but you may want to download a + newer version from <a class="ulink" href="http://www.ftdichip.com/FTDrivers.htm" target="_top">http://www.ftdichip.com/FTDrivers.htm</a>. + </p></div><div class="section" title="2. Downloading Micro Peak data"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1986896"></a>2. Downloading Micro Peak data</h2></div></div></div><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> + Connect the MicroPeak USB adapter to a USB cable and plug it + in to your computer. + </p></li><li class="listitem"><p> + Start the MicroPeak application, locate the File menu and + select the Download entry. + </p></li><li class="listitem"><p> + The MicroPeak USB adapter has a small phototransistor on the + end of the board furthest from the USB connector. Locate + this and place the LED on the MicroPeak right over + it. Turn on the MicroPeak board and adjust the position + until the blue LED on the MicroPeak USB adapter blinks in + time with the orange LED on the MicroPeak board. + </p></li><li class="listitem"><p> + After the maximum flight height is reported, MicroPeak will + pause for a few seconds, blink the LED four times rapidly + and then send the data in one long blur on the LED. The + MicroPeak application should receive the data. When it does, + it will present the data in a graph and offer to save the + data to a file. If not, you can power cycle the MicroPeak + board and try again. + </p></li></ul></div></div><div class="section" title="3. Analyzing MicroPeak Data"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3318344"></a>3. Analyzing MicroPeak Data</h2></div></div></div><p> + The MicroPeak application can present flight data in the form + of a graph, a collection of computed statistics or in tabular + form. + </p><p> + MicroPeak collects raw barometric pressure data which is + then used to compute the remaining data. Altitude is computed + through a standard atmospheric model. Absolute error in this + data will be affected by local atmospheric + conditions. Fortunately, these errors tend to mostly cancel + out, so the error in the height computation is much smaller + than the error in altitude would be. + </p><p> + Speed and acceleration are computed by first smoothing the + height data with a Gaussian window averaging filter. For speed + data, this average uses seven samples. For acceleration data, + eleven samples are used. These were chosen to provide + reasonably smooth speed and acceleration data, which would + otherwise be swamped with noise. + </p><p> + Under the Graph tab, the height, speed and acceleration values + are displayed together. You can zoom in on the graph by + clicking and dragging to sweep out an area of + interest. Right-click on the plot to bring up a menu that will + let you save, copy or print the graph. + </p><p> + The Statistics tab presents overall data from the flight. Note + that the Maximum height value is taken from the minumum + pressure captured in flight, and may be different from the + apparant apogee value as the on-board data are sampled twice + as fast as the recorded values, or because the true apogee + occurred after the on-board memory was full. Each value is + presented in several units as appropriate. + </p><p> + A table consisting of the both the raw barometric pressure + data and values computed from that for each recorded time. + </p><p> + The File menu has operations to open existing flight logs, + Download new data from MicroPeak, Save a copy of the flight + log to a new file, Export the tabular data (as seen in the Raw + Data tab) to a file, change the application Preferences, Close + the current window or close all windows and Exit the + application. + </p></div><div class="section" title="4. Configuring the MicroPeak application"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp785616"></a>4. Configuring the MicroPeak application</h2></div></div></div><p> + The MicroPeak application has a few user settings which are + configured through the Preferences dialog, which can be + accessed from the File menu. + </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p> + The Log Directory is where flight data will be saved to + and loaded from by default. Of course, you can always + navigate to other directories in the file chooser windows, + this setting is just the starting point. + </p></li><li class="listitem"><p> + If you prefer to see your graph data in feet and + miles per hour instead of meters and meters per second, + you can select Imperial Units. + </p></li><li class="listitem"><p> + To see what data is actually arriving over the serial + port, start the MicroPeak application from a command + prompt and select the Serial Debug option. This can be + useful in debugging serial communication problems, but + most people need never choose this. + </p></li><li class="listitem"><p> + You can adjust the size of the text in the Statistics tab + by changing the Font size preference. There are three + settings, with luck one will both fit on your screen and + provide readable values. + </p></li><li class="listitem"><p> + The Look & feel menu shows a list of available + application appearance choices. By default, the MicroPeak + application tries to blend in with other applications, but + you may choose some other appearance if you like. + </p></li></ul></div><p> + </p><p> + Note that MicroPeak shares a subset of the AltosUI + preferences, so if you use both of these applications, change + in one application will affect the other. + </p></div></div><div class="chapter" title="Chapter 4. Technical Information"><div class="titlepage"><div><div><h2 class="title"><a name="idp3018560"></a>Chapter 4. Technical Information</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#idp3018880">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp3020504">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp3022056">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp3023856">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp3025920">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp3027624">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp52184">7. MicroPeak Programming Interface</a></span></dt></dl></div><div class="section" title="1. Barometric Sensor"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3018880"></a>1. Barometric Sensor</h2></div></div></div><p> MicroPeak uses the Measurement Specialties MS5607 sensor. This has a range of 120kPa to 1kPa with an absolute accuracy of 150Pa and a resolution of 2.4Pa. @@ -115,9 +234,9 @@ NAR #88757, TRA #12200<br> </p><p> Ground pressure is computed from an average of 16 samples, taken while the altimeter is at rest. Flight pressure is - computed from an exponential IIR filter designed to smooth out - transients caused by mechanical stress on the barometer. - </p></div><div class="section" title="2. Micro-controller"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1961960"></a>2. Micro-controller</h2></div></div></div><p> + computed from a Kalman filter designed to smooth out any minor + noise in the sensor values. + </p></div><div class="section" title="2. Micro-controller"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3020504"></a>2. Micro-controller</h2></div></div></div><p> MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny CPU contains 8kB of flash for the application, 512B of RAM for temporary data storage and 512B of EEPROM for non-volatile @@ -128,9 +247,9 @@ NAR #88757, TRA #12200<br> this mode, the chip consumes only .1μA of power. MicroPeak uses this mode once the flight has ended to preserve battery power. - </p></div><div class="section" title="3. Lithium Battery"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp2901888"></a>3. Lithium Battery</h2></div></div></div><p> + </p></div><div class="section" title="3. Lithium Battery"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3022056"></a>3. Lithium Battery</h2></div></div></div><p> The CR1025 battery used by MicroPeak holes 30mAh of power, - which is sufficient to run for over 15 hours. Because + which is sufficient to run for over 40 hours. Because MicroPeak powers down on landing, run time includes only time sitting on the launch pad or during flight. </p><p> @@ -141,11 +260,11 @@ NAR #88757, TRA #12200<br> battery holder. A small pad on the circuit board makes contact with the negative battery terminal. </p><p> - Shipping restrictions prevent us from including a CR1025 - battery with MicroPeak. Many stores carry CR1025 batteries as - they are commonly used in small electronic devices such as - flash lights. - </p></div><div class="section" title="4. Atmospheric Model"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1674792"></a>4. Atmospheric Model</h2></div></div></div><p> + Shipping restrictions may prevent us from including a CR1025 + battery with MicroPeak. If so, many stores carry CR1025 + batteries as they are commonly used in small electronic + devices such as flash lights. + </p></div><div class="section" title="4. Atmospheric Model"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3023856"></a>4. Atmospheric Model</h2></div></div></div><p> MicroPeak contains a fixed atmospheric model which is used to convert barometric pressure into altitude. The model was converted into a 469-element piece wise linear approximation @@ -161,7 +280,7 @@ NAR #88757, TRA #12200<br> altitude is subtracted from the computed apogee altitude, so the resulting height is more accurate than either the ground or apogee altitudes. - </p></div><div class="section" title="5. Mechanical Considerations"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1421872"></a>5. Mechanical Considerations</h2></div></div></div><p> + </p></div><div class="section" title="5. Mechanical Considerations"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3025920"></a>5. Mechanical Considerations</h2></div></div></div><p> MicroPeak is designed to be rugged enough for typical rocketry applications. It contains two moving parts, the battery holder and the power switch, which were selected for their @@ -177,4 +296,65 @@ NAR #88757, TRA #12200<br> any direction. Because it is a sliding switch, orienting the switch perpendicular to the direction of rocket travel will serve to further protect the switch from launch forces. + </p></div><div class="section" title="6. On-board data storage"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3027624"></a>6. On-board data storage</h2></div></div></div><p> + The ATtiny85 has 512 bytes of non-volatile storage, separate + from the code storage memory. The MicroPeak firmware uses this + to store information about the last completed + flight. Barometric measurements from the ground before launch + and at apogee are stored, and used at power-on to compute the + height of the last flight. + </p><p> + In addition to the data used to present the height of the last + flight, MicroPeak also stores barometric information sampled + at regular intervals during the flight. This information can + be extracted from MicroPeak through any AVR programming + tool. + </p><div class="table"><a name="idp3028936"></a><p class="title"><b>Table 4.1. MicroPeak EEPROM Data Storage</b></p><div class="table-contents"><table summary="MicroPeak EEPROM Data Storage" border="1"><colgroup><col align="center" class="Address"><col align="center" class="Size (bytes)"><col align="left" class="Description"></colgroup><thead><tr><th align="center">Address</th><th align="center">Size (bytes)</th><th align="center">Description</th></tr></thead><tbody><tr><td align="center">0x000</td><td align="center">4</td><td align="left">Average ground pressure (Pa)</td></tr><tr><td align="center">0x004</td><td align="center">4</td><td align="left">Minimum flight pressure (Pa)</td></tr><tr><td align="center">0x008</td><td align="center">2</td><td align="left">Number of in-flight samples</td></tr><tr><td align="center">0x00a … 0x1fe</td><td align="center">2</td><td align="left">Instantaneous flight pressure (Pa) low 16 bits</td></tr></tbody></table></div></div><br class="table-break"><p> + All EEPROM data are stored least-significant byte first. The + instantaneous flight pressure data are stored without the + upper 16 bits of data. The upper bits can be reconstructed + from the previous sample, assuming that pressure doesn't + change by more more than 32kPa in a single sample + interval. Note that this pressure data is <span class="emphasis"><em>not</em></span> + filtered in any way, while both the recorded ground and apogee + pressure values are, so you shouldn't expect the minimum + instantaneous pressure value to match the recorded minimum + pressure value exactly. + </p><p> + MicroPeak samples pressure every 96ms, but stores only every + other sample in the EEPROM. This provides for 251 pressure + samples at 192ms intervals, or 48.192s of storage. The clock + used for these samples is a factory calibrated RC circuit + built into the ATtiny85 and is accurate only to within ±10% at + 25°C. So, you can count on the pressure data being accurate, + but speed or acceleration data computed from this will be + limited by the accuracy of this clock. + </p></div><div class="section" title="7. MicroPeak Programming Interface"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp52184"></a>7. MicroPeak Programming Interface</h2></div></div></div><p> + MicroPeak exposes a standard 6-pin AVR programming interface, + but not using the usual 2x3 array of pins on 0.1" + centers. Instead, there is a single row of tiny 0.60mm × + 0.85mm pads on 1.20mm centers exposed near the edge of the + circuit board. We couldn't find any connector that was + small enough to include on the circuit board. + </p><p> + In lieu of an actual connector, the easiest way to connect to + the bare pads is through a set of Pogo pins. These + spring-loaded contacts are designed to connect in precisely + this way. We've designed a programming jig, the MicroPeak + Pogo Pin board which provides a standard AVR interface on one + end and a recessed slot for MicroPeak to align the board with + the Pogo Pins. + </p><p> + The MicroPeak Pogo Pin board is not a complete AVR programmer, + it is an interface board that provides a 3.3V regulated power + supply to run the MicroPeak via USB and a standard 6-pin AVR + programming interface with the usual 2x3 grid of pins on 0.1" + centers. This can be connected to any AVR programming + dongle. + </p><p> + The AVR programming interface cannot run faster than ¼ of the + AVR CPU clock frequency. Because MicroPeak runs at 250kHz to + save power, you must configure your AVR programming system to + clock the AVR programming interface at no faster than + 62.5kHz, or a clock period of 32µS. </p></div></div></div></body></html> |