POT4b

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Also see : POT4 and POT4a

POT4b is a bridge type differential amplifier with signal processing and a precision voltage 2.500V reference.

revisions from POT4a

• changed reference from TL1431 to fixed voltage MAX1631
• added circuit to make REF- and REF+ approximately symmetric about COM
• instrumentation amplifier is INA122 - which has a gain bandwidth product of ~ 200KHz. Thus board acts like an amplifer with fixed gain of 200K/RA1 followed by a 1st order LP at frequency RA1, followed by a 2nd order LP at frequency 1.6KHz (or 497 Hz).

gain and filter variations

• default gain 502x, amp cut-off 400Hz, LP2 cut-off freq of 1.6KHz, amplifier cut-off

• B1,B2 gain 502x, amp cut-off 400 Hz, LP2 cut-off = 497 Hz. CC1=0.1u, Cm1,Cm2 = 9.1nF
• B2 gain 980x (RA w 205 ohm) , amp cut-off 204 Hz, LP2 cut-off = 497 Hz
• B4 gain 4005x, amp cut-off 50 Hz, LP2 cut-off = 497 Hz

Identification

top side

bottom side

• POT4b is a green PCB with white silk screen on two sides.
• On top side is labeled "POT4B 061605"
• Dimensions 1.75" x 0.85"
• Two mounting holes (diameter = 0.125"), top side clearance > 0.25"
• The color of DL1,DL2 indicates the input configuration of the board

Led Indicators

• (DL1, DL2) : A pair of single LEDs indicate the present of power. These LEDs are aligned with the power input to the boards.
• DK1 : The intensity of this dual RED/GREEN LED indicates the voltage of the "position signal".

board status / history

• 4-5-06 : B5 when powered by CEB and Greddy smokes RN1 and associated PCB trace. Replaced and controlled power to board to discover that UA1 gets hot. Most likly power was applied to the input side of the board and destroyed the device.

• 3-15-05 : B3 has power application problem.

Design Files

• Media:Pot4b-sch-revb-062205.pdf
• Media:Rpot4b-pcb-top-revb-061605.pdf
• Media:Rpot4b-pcb-bot-revb-061605.pdf
• Gerber files and Tango DOS source (6-16-05)

Bill of Materials

Bill of Materials