> > Did you build the accelerometer from "scratch," or did you just > augment a commercially available accelerometer? Either way, I'd > appreciate a little blurb about what you did. I'm going to be needing > an accelerometer at some point and have had trouble finding one that > does what I need but doesn't cost $500. (I need three for a student > project...) > > Chris Kristof > Junior ECE > Carnegie Mellon University > Hello Chris, I use an Analog devices ADXL50 accelerometer. It is an excellent product which cost me $75 about 10 months ago. Accelerometers are generally coming down in price. I will send you a list of manufacturers at the end of this post. Back to my device. I use the Analog Devices part because it is very small (TO-5 can I think). It is very linear, has a built in unused amp that the designer can use for several puposes, etc. Get the data sheet on it, I think you will like it. I use the PIC16C71 because it had an A/D converter on board. It is very small, has a bigger stack, and you don't have to do all that page switching stuff if you do far calls in the program. I save the data to EEPROM. I am currently using two 93c66 for a total of 1024 samples. I wrote the software to buffer 20 samples in a rotating ram buffer, and if the last five samples all exceed 2 G's, then I set a flag that means liftoff of the rocket has been detected. I then start saving subsequent samples to EEPROM starting with the 21 position. Once the EEprom is full, I go back and save the buffered data in the first 20 positions of the EEPROM. This way, I see a small section where the rocket is sitting on the pad, then I see the liftoff etc. After all this is complete, The device goes to sleep. I recover the rocket, pull the EEPROMs and put them in another device that uses a 16C71 and a Maxim RS232 converter chip. I wrote software to do 9600 baud transfer, and to convert the data to ascii. What I get is a stream of numbers that can be directly pasted into my spreadsheet for plotting. It works extremely well and I have been asked to make it available to the rocket hobby industry. The version I'm working on now will use Microchips new EEPROMs, the 24LC65 that have 8k. Also, I will use a 10 bit, serial A/D converter for better resolution, and I will include a small Dallas Semiconductor RS232 converter on the same board. The Dallas part steals -12 volts from the host computer in order to transmit it's data without charge pump circuitry to make the negative voltage. The whole thing will be very small, since I will try to get most of the parts in the surface mount package. Anymore questions, let me know. Regards, Jerry Here is the promised list of acclerometers: >>>>>>>>>>>>>>>> List of Accelerometer Manufacturers <<<<<<<<<<<<<<<<<<<<<< ------------------------------- Analog Devices ADXL50 accelerometer. Power Supply........................... +5V (+/- 5%) Measurement Range...................... +/- 50g Pre-Amp Zero-g output level............ +1.8V Pre-Amp output span.................... +1.8V (+/-1.2V) at +/-50g Uncommitted amp output range........... +0.25V to +4.75V Overall Accuracy....................... 5% of Full Scale Linearity.............................. 0.5% of Full Scale Bandwidth.............................. DC to 1kHz Voltage Noise (p-p) at BW = 0.3kHz..................... +/-0.24% of Full Scale at BW = 1.0kHz..................... +/-0.48% of Full Scale Transverse Sensitivity................. 2% Unpowered Shock Survival............... 2000g I've found several Distributors: Newark Electronics..................... 1-800-281-4320 Hamilton-Hallmark...................... 1-800-332-8638 Active Electronics..................... 1-800-677-8899 ******************************* Silicon Designs, Inc. - Capacitive Accelerometers Model 1010, Digital output: Produces Digital pulse train in which the density of pulses (number of pulses a second) is proprtional to applied acceleration. It operates with a single +5 volt power supply and requires a clock of 100kHz - 1MHz. The output is ratiometric to the clock frequency and independent of the power supply voltage. Two forms of digital signals are provided for direct interfacing to a microprocessor or counter. This devices comes in a PLCC package that is smaller than a penny. Model 1210, Analog output: Privides two analog outputs, 1-4 volts, or 4-1 volt, with O g's at 2.5 volts. The outputs can be used either differentially or single ended referenced to 2.5 volts. Two reference voltages--+5.0 and +2.5 volts (nominal)-- are required; the output scale factor is ratiometric to the +5 volt reference voltage. Address: Silicon Designs, Inc. 1445-NW Mall Street Issaquah, WA. 98027-5344 Tel: (206) 391-8329 Fax: (206) 391-0446 Prices start at about $100 and they offer a digital accelerometer evaluation board for $200. *********************************** Silicon Microstructures, Inc. Model 7170 series and 7130 series capacitive accelerometers. These are relatively large devices with built in ASIC signal processing.They have very good accuracy specs and are pre-calibrated. I have not contacted them personally but they will send you some brochures on all of their devices. They also make pressure sensors. Address: Silicon Micostructures, Inc. 46725 Fremont Boulevard Fremont CA. 94538 Tel: (510) 490-5010 Fax: (510) 490-1119 ********************************************************************* ICSensors ---------- Address: ICSensors 1701 McCarthy Blvd. Milpitas, CA 95035-7416 Tel. (800) 767-1888 (408) 432-1800 Fax. (408) 434-6687 --------------------------------------------- Model 3145 Signal Conditioned Temperature Compensated 0.5 to 4.5 Vdc Output, Low Cost ( this is a relative statement ) 2g, 5g, 10g, 20g, 50g, 100g, 200g ranges $230 for 1 --------------------------- Model 3140 Instrumentation grade Signal Conditioned Temperature Compensated 0.5 to 4.5 Vdc Output 2g, 5g, 10g, 20g, 50g, 100g, 200g ranges $295 for 1 --------------------------- Model 3031 OEM Accelerometer Piezoresistive low cost Surface mount package 2g, 5g, 10g, 20g, 50g, 100g, 200g, 500g ranges $74 for 1 --------------------------- Model 3021 and 3026 OEM Accelerometer Piezoresistive low cost 2g, 5g, 10g, 20g, 50g, 100g, 200g, 500g ranges price ranges from 98 - 141 for 1, depending on g range *************************************************************************** Endevco Corporation 30700 Rancho Viejo Road San Juan Capistrano, CA 92675 Tel. (714) 493-8181 Fax. (714) 661-7231 ---------------------------- Variable Capacitance and Piezoresistive Accelerometers many models, contact Endevco for literature. *************************************************************************** AMP P.O. Box 799 Valley Forge, PA 19482 Tel. (610) 666-3500 Fax. (610) 666-3509 -------------------------- Piezo Film accelerometer Sensors If you contact AMP, they will send you alot of information on their piezo sensors and include a little piezo film sensor for you to experiment with. Their most interesting device is the AHC-04-08 accelerometer/shock sensor that contains three sensing elements oriented to measure acceleration in two linear axes and one angular axis. Each sensor has a dedicated channel with adjustable gain, an adjustable comparator, and selectable output control to provide either a digital or analog signal. It is a low profile surface mount chip with 14 pins. It has internal eeprom for programming the adjustable gains, and output modes. The only problem I see with this device is that it has a lower limit on the frequency response. Typically about 7-13 Hz. This means if it were subjected to a steady 10 G acceleration for example, the output would rise to 10 G's then decay down to zero even though it were still at 10 G's. This is good for measuring shocks but not steady accelerations. A good point is that it was only $30 for a single unit. **************************************************************************