OPTOFAST-2

Features

• Opto-Isolator card
• 4-Channels
• 4N25 Optoisolators
• Input /Output isolation
• Transistor driver for Opto LED reduces required drive from 10 mA to under 500 uA
• Input channels share their own common VCC/Ground
• Output channels share their own common Vcc/Ground
• 8-pin header for input
• 8-pin header for output
• Configuration Options
  • Speed enhanced
  • Bypass Input transistors
  • Remove Output collector resistors
• 49x49mm
• (4) 4-40 mounting holes

Schematic (One channel)

• U1 represents U1-U4 (channels 1-4)
• Q1 represents Q1-Q4 (channels 1-4)
• R1 (VCC) represents R1,R4,R7,R10 (channels 1-4)
• R2 (DIR) represents R2,R5,R8,R11 (channels 1-4)
• R3 (BASE) represents R3,R6,R8,R12 (channels 1-4)
• R13 (FAST) represents R13-R16 (channels 1-4)
• R17 (COLL) represents R17-R20 (channels 1-4)

Input Options

• Refer to schematic for impact of options

Use Input Transistor - Standard Option

• Common VCC in option
• Install transistor Q1
• R1 = 150
  • LED current is 3.5V/150 Ohms = 23 mA
  • CTR = .20, 4.7 mA
• R2 = Do not populate
• R3 = 10K
  • Base drive ~ (Vin - 0.7V)/R3
  • At 5V drive this is 4.3V/R3
    • Using R3=10K at 5V this is 0.43mA Ib
    • HFE (MMBT3904) = 100 min
    • That is potentially 43 mA (in the switching range of the transistor)
      • Collector resistor and LED voltage drop are current limiter
  • At 3.3V drive this is (3.3-0.7)/10K = .26mA Ib
    • HFE = 100 min
    • That is 26 mA (in the switching range of the transistor)
• H1 do not short

Direct Drive - Special Option

• Do not install Q1
• Do not install R1
• R2 = 150
  • Input current = LED current = 3.5V/150 Ohms = 23 mA
• Do not install R3
• Do not install Q1
• Short H1

Output Options

Standard Output

• R17 = 1.2K
  • 5V/1.2K = 4.1mA of output transistor B-E current
  • Leaves 4.7-4.1 mA = 600 uA of output low current

Open Collector Output - Special Option

• Do not install R17

Fast Option - Standard

• R13 = 20K (empirically determined from the scope eye)

Connectors

P1 - Input

8-pin, right angle, 0.1" pitch

1. Vcc (In)
2. Vcc (In)
3. IN 1
4. IN 2
5. IN 3
6. IN 4
7. GND (In)
8. GND (In)

P2 - Output

8-pin, right angle, 0.1" pitch

1. Vcc (Out)
2. Vcc (Out)
3. OUT 1
4. OUT 2
5. OUT 3
6. OUT 4
7. GND (Out)
8. GND (Out)

Calculations

Power Domains

• Each side of the card has its own independent power domain
• Each side of the card receives external power
• Each side can be powered with 3.3V or 5V

Input Drive Calculations

• The input side of the card has optional drive transistors
  • 10K ohm resistors into the transistor base allows for wide input voltage range
  • If the input signals are 5V, then the input current is 500uA

Output Drive Calculations

• Output side of the card has 4.7K pullups
  • These determine the rise time of the output

These are the calculations for the output current:

Input Side
Vcc (IN)	5	V
Vf	1.2	V
Vres	3.8	V
Res	150	Ohms
If	25.33	mA
CT	0.2	A/A
Iout max	5.07	mA
Output side
Vcc (OUT)	5	V	3.3	V
Rballast	4.7	Kohms	4.7	Kohms
Iballast	1.06	mA	0.70	mA
IL out avail	4.00	mA	4.36	mA
Input Side
Vcc (IN)	3.3	V
Vf	1.2	V
Vres	2.1	V
Res	150	Ohms
If	14.00	mA
CT	0.2	A/A
Iout max	2.80	mA
Output side
Vcc (OUT)	5	V	3.3	V
Rballast	4.7	Kohms	4.7	Kohms
Iballast	1.06	mA	0.70	mA
IL out avail	1.74	mA	2.10	mA

Test Card Measurements

Setup

• Goal was to determine the performance of the OPTOFAST card
• 5V operation
• Same 5V input/output power supply
• Each of the channels were configured uniquely/individually
• MHS-5200A - Digital DDS Dual-channel Signal Generator
  • 1 KHz square wave
  • 5V signal level
• Single channel checked at a time
• Oscilloscope
  • Rigol DS1054Z
  • 50 MHz
  • Ultra Sigma software used for screen captures

Notes

• Note that the input buffer transistor inverts the signal
• Built a card that has four different configurations
• Options
  • Fast/Slow
  • Direct drive input LED/Transistor Buffered input

Test Results

Channel	Fast/Slow	TransBuff/Direct	Input Rise/Fall	Time(uS)
1	Slow	Transistor Buffer	Fall	28.6
1	Slow	Transistor Buffer	Rise	1.8
2	Fast	Transistor Buffer	Fall	6.68
2	Fast	Transistor Buffer	Rise	3.6
3	Slow	Direct Input	Fall	1.84
3	Slow	Direct Input	Rise	27.4
4	Fast	Direct Input	Fall	4.24
4	Fast	Direct Input	Rise	5.28

Observations

• Input Transistor effect
  • Value of the input transistor is that does not require a high drive level input
  • The input transistor has very little effect on speed - a couple hundred nS slower than direct drive
  • The inversion effect of the input transistor moves the "slow" time around
  • Downside of the input transistor is that it has less noise immunity since the transistor turns on at 0.6V vs the internal LED in the optocoupler at 1.5V?
• Output "fast" circuit
  • Output pullup of 4.7K affects the rise time of the output
  • The fast is faster, but not in some conditions
  • Average of rise/fall is better
  • Transistor buffer instance rise input is slower with the fast output
  • Fast output helps the output rise time

Ch1-Slow-NPNBuffer-InFall

Ch1-Slow-NPNBuffer-InRise

Ch2-Fast-NPNBuffer-InFall

Ch2-Fast-NPNBuffer-InRise

Ch3-Slow-Direct-InFall

Ch3-Slow-Direct-InRise

Ch4-Fast-Direct-InFall

]

Ch4-Fast-Direct-InRise

Factory Test

• ODAS Card Test Station
  • Running ODASTESTER code
• DB37RIBBON
• Cable set
• PC running PuTTY
  • 9600 baud
  • USB-C cable
    • USB connected to PC and USB-C connected to BLACK-PILL-HUB
• Powered through the USB-C connector on the STM32 Black Pill

Checking if EEPROM is present on UUT...EEPROM is not present on UUT
Count of I2C devices in range 0x20-0x27 on UUT = 0
No external I2C mux card
Select the board type (Other)
4 - OPTOFast/Small Non-Inverting board
5 - OPTOFast/Small Inverting board
6 - OptoFastBi board
Select board > 5
C=Card Tests, D=Direct, E=EEPROM, I=access Internal DIGIO32
L=Loop/S=Single, T=Test, B=Bounce LEDs, I=UUT Int'l Tests, X=eXit sub-menu
Testing UUT = Opto Inc
Error on port 0 Expected Low
Test PASS = 0, FAIL = 1

Layout

Assembly Sheet

• OptoFast Assembly Sheet
• OPTOFAST-2 Assembly Sheet