Pcb Logic

A look at what is currently available on eBay


PCB Logic Board WDC WD2500SD 01KCB0 488397168
PCB Logic Board WDC WD2500SD 01KCB0 488397168
US $19.99
 PCB Logic Board Hitachi IC35L040AVVN070-0 7N8450 9SRE
PCB Logic Board Hitachi IC35L040AVVN070-0 7N8450 9SRE
US $9.99
 Toshiba SATA 160GB MK1655GSX PCB LOGIC BOARD (H27-10)
Toshiba SATA 160GB MK1655GSX PCB LOGIC BOARD (H27-10)
US $30.00
PCB Logic Board Hitachi HTS541060G9SA00 DA1488
PCB Logic Board Hitachi HTS541060G9SA00 DA1488
US $19.99
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H27-11)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H27-11)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H34-09)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H34-09)
US $30.00
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-04)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-04)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-01)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-01)
US $30.00
 Toshiba 250GB SATA MK2555GSX, PCB LOGIC BOARD (H18-08)
Toshiba 250GB SATA MK2555GSX, PCB LOGIC BOARD (H18-08)
US $35.00
Toshiba 250GB SATA MK2555GSX PCB LOGIC BOARD (H18-12)
Toshiba 250GB SATA MK2555GSX PCB LOGIC BOARD (H18-12)
US $35.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-09)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-09)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-04)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-04)
US $30.00
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H27-14)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H27-14)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H27-12)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H27-12)
US $30.00
 Toshiba SATA 160GB MK1655GSX PCB LOGIC BOARD (H27-08)
Toshiba SATA 160GB MK1655GSX PCB LOGIC BOARD (H27-08)
US $30.00
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H34-08)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H34-08)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H34-15)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H34-15)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-02)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-02)
US $30.00
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-03)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H35-03)
US $30.00
 Toshiba 250GB SATA MK2555GSX, PCB LOGIC BOARD (H18-09)
Toshiba 250GB SATA MK2555GSX, PCB LOGIC BOARD (H18-09)
US $35.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-07)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-07)
US $30.00
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-03)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-03)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-08)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-08)
US $30.00
 Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-06)
Toshiba SATA 160GB MK1655GSX, PCB LOGIC BOARD (H43-06)
US $30.00

Pcb Logic
why is logic ground connected to protective earth ?

take a digital printed circuit board, such as main board of a PC, you can observe that signal ground is connected to protective earth, when you touch the casing you are actually touching the logic "0" of the microchips on the PCB; are these two connected together to provide a common reference for any communication between PCs via RS232, USB or parallel port ? Could there be any other reason than providing a common reference for communicating PCs ?

Logic ground connected to protective (safety) ground is done by habit more than convention. IMHO is a bad habit due to the fact that the earth ground MUST be connected to earth to ensure shock protection. It would be better if all signal RETURNS (+3.3V, analog, digital, RS-232) were isolated and connected only where mixed signals occur. This is what is known as isolation. Most AC circuits have input sides that are isolated with transformers and that are controlled by opto-isolators. This is for safety. In addition, UL code does not allow for 'mains' neutrals to be connected to earth returns or grounds. Otherwise it would defeat the purpose of having a seperate earth return circuit.

The most critical aspect of earth return is that it must be of the lowest impedance of any path in the design. A minimum requirement is usually spec'd to handle 10A continously .

For RS-232, it is tricky since you only want one side of the shield connected to earth. Otherwise you will suffer from ground loops and hamper your common mode rejection. As a rule, the higher power deivce with the lowest return path to earth ground should be used to connect shield, but only one side. In cases where the are close, pick the Data Terminal Equiptment (DTE - computer), not the Data Communications Equipment (DCE - modem).

The tricky area is for mixed signals where analog and digital cross. Here is where a very simple (small) jumper is required just at the converter to all small currents for the converter to flow. So if you are using a +3.3V micro that is connected to a +12V ADC, then design in a resistor where the converter is to connect the analog and digital returns. If you have problems and need to isolate noise, you will thank me later. ;-)

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January 18th, 2010 in PCs & PC Add-Ons | tags: , , , , , , , , , , ,

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