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Showing posts with label usb. Show all posts
Showing posts with label usb. Show all posts

USB Powered PIC Programmer

Posted by Unknown Thursday, October 3, 2013 0 comments
This simple circuit can be used to program the PIC16F84 and similar "flash memory" type parts. It uses a cheap 555 timer IC to generate the programming voltage from a +5V rail, allowing the circuit to be powered from a computer’s USB port. The 555 timer (IC1) is configured as a free-running oscillator, with a frequency of about 6.5kHz. The output of the timer drives four 100nF capacitors and 1N4148 diodes wir-ed in a Cockroft-Walton voltage multiplier configuration.

USB-Powered PIC Programmer circuit schematic

The output of the multiplier is switched through to the MCLR/Vpp pin of the PIC during programming via a 4N28 optocoupler. Diodes ZD1 and D5 between the MCLR/Vpp pin and ground clamp the output of the multiplier to about 13.6V, ensuring that the maximum input voltage (Vihh) of the PIC is not exceeded. A 100kΩ resistor pulls the pin down to a valid logic low level (Vil) when the optocoupler is not conducting. The circuit is compatible with the popular "JDM" programmer, so can be used with supporting software such as "ICProg" (see http://www.ic-prog.com).
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USB cable signals

Posted by Unknown Saturday, April 6, 2013 0 comments
USB cable consists of 4 wires plus a conductor wire wrapping, such as the protectors are usually found in the audio cable. Cable number 1 is used to channel resources to the voltage of 5 volts, if necessary USB devices may draw power from this line and should not exceed 100 mA. Computer equipped with USB capability, is required to provide power at 100 mA for this purpose. USB devices that require more power than the aforementioned provisions, must provide their own resources for the purposes work equipment.


The USB cable signals
The USB cable signals

Number 4 is the ground cable as a back channel source voltage of 5 volts. Cable number 2 and number 3 is used for signal transmission. No. 2 cable and cable called D-3 numbers called D, the voltage on the two channels is changed between 0 Volt and 3.3 Volt. Digital signal is sent through the two channels are said to be difference signal, which means that the signal digital 0 or 1 is not declared to the magnitude of the voltage on the channel to the ground, as well as digital signals used in the IC TTL (transistor Transitor Logic) or the RS232 channel.

Digital signal is expressed by the voltage difference between the two cables. If the voltage on the D channel is higher than the voltage at D-channel, then the information transmitted digital signal is 1 , otherwise the digital signal 0 is expressed by the voltage at D <voltage at D-. To distinguish the speed of data transmission, the channel USB devices attached to the 3.3 Volt prisoners in different ways, as shown in Fig.

At low speed USB devices, the D-channel to 3.3 Volt dipasangan custody, or in the absence of information transmission, the channel is in state 0 . For full speed USB device, such resistance is connected to the D channel, so that in the absence of data transmission channels are in state 1 .
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