This device is designed to measure the torque in an automobile drive shaft and provide an output to a vehicle data recording system or a portable computer via an RS-232 interface. The received data can then be combined with RPM measurements from the data recording system to calculate horsepower. It consists of the sensor unit, (Figure 1), which attaches to the driveshaft, and the receiver unit, , which provides the serial output signal. The sensor unit is battery powered and communicates with the receiver via a 433 Mhz RF data link.The receiver unit is powered by the vehicle electrical system. Circuit operation is shown in the diagram.
Posted on Monday, May 23, 2011 • Category: Power Supplies
The linear laboratory power supply, shown in the schematic, provides 0-30 volts, at 1 amp current, using a discrete transistor regulator with op-amp feedback to control the output voltage. The supply was constructed in 1975 and has a constant current mode that can be used to recharge batteries. With reference to the schematic, lamp, LP2, is a power-on indicator. The other lamp (lower) lights when the unit reaches its preset current limit. R5, C2, and Q10 (TO-3 case) operate as a capacitor multiplier. The 36 volt zener across C2 limits the maximum supply voltage to the op-amps supply pins. D5, C4, C5, R15, and R16 provide a small amount of negative supply for the op-amps so that the op-amps can operate down to zero volts at the output pins (pins 6). A more modern design might eliminate these 4 components and use a CMOS rail-to-rail op-amp. Current limit is set by R3, D1, R4, R6, Q12, R10, and R13 providing a bias to U2 that partially turns off transistors Q9 and Q11 when the current limit is reached. R4 is a front panel potentiometer that sets the current limit, R22 is a front panel potentiometer that sets the output voltage (0-30 volts), and R11 is an internal trim-pot for calibration. The meter is a 1 milliamp meter with an internal resistance of 40 ohms. Switch S1 determines whether the meter reads 0-30 volts, or 0-1 amp.
Posted on Monday, May 23, 2011 • Category: RC Servo Motors
The USB-Servo is a device to control a servo via USB. A servo is a motorized device that is commonly used in remote controlled cars and planes. I built this device to activate a toy puppet. The puppet has a button on its bottom, if you press the button the puppet collapses. When the computer is able to press the button, I can use the puppet to signal information like someone's online-state in the Jabber-network: when my friend goes online, the puppet stands up, when he logs off it collapses.
Servos are connected with three-wire-cables. A red and a black one for the power, and a yellow one for the signal. Power has to be between 4.8 and 6 volts, so the 5 volts from the USB-port is in the range. The signal doesn't take much current, so you can connect it directly to the controller. The angle of the servo is controlled with pulse width modulation (PWM). It gets a signal of about 50Hz (one pulse every 20ms), the length of the pulse tells the servo the angle to adjust.
Posted on Sunday, May 22, 2011 • Category: Motor Controllers
Here is a very simple project of controlling a small DC-motor (taken from an old personal cassette player) with ATmega8. The ATmega8 is having three PWM channels, out of which two are used here. PWM waveforms are fed to MOSFET (RFD3055) H-bridge.
Here, direction is controlled using a two-position toggle switch and speed of the motor is controlled by two push-buttons, one for increasing the speed and other for reducing.
The schematic is geiven here (click on the image to enlarge):
When switch SW1 is closed, OC1A channel is active which will feed the PWM signal to Q1 & Q4 MOSFETs. The OC1B pin will remain low keeping the Q3 & Q2 in OFF condition. When SW1 is toggled to open position, OC1A pin will become low, making Q1 & Q4 OFF and OC1B will feed the PWM signal to Q3 & Q2, resulting in the change in the direction of current flow through motor. Hence, motor rotation direction will change.
The speed is controlled by Push-buttons S2 & S3. Pressing S2 will increase the speed in fixed steps. Similarly, pressing S3 will reduce the speed in fixed steps.
Circuit-Zone.com © 2020. All Rights Reserved.