Opto interrupter circuit re-design - advice sought - UK Vintage Radio Repair and Restoration Discussion Forum

ianm · 29th Aug 2018, 7:32 pm

This is related to my earlier thread entitled "Driver board for piano roll perforator machine", in the Modern Technology section. Aside of a general requirement to bring the machine's circuitry up to date, there is an immediate requirement to replace an opto interrupter board that has snapped in two.

A repair has been attempted by my friend who owns it, without success, so I'm looking to build a new board from scratch. It doesn't justify a custom PCB, so I would just use Vero board and arrange the components appropriately. It's a basic circuit, but two main components are obsolete, so I'm looking to use some up-to-date replacements and to alter the circuit to suit. However, although I've constructed many circuits over the years, I don't really have any design capability, hence I am seeking guidance on how to proceed.

Attached is a circuit diagram. The component that I'm very unlikely to find is the op-amp and I'm thinking that perhaps a 741 might be a viable alternative. The P507A sensor is obsolete too, but I suspect that this would be much easier to substitute than the op-amp. A data sheet is readily available for the sensor, from the Toshiba website.

Any assistance much appreciated.

TonyDuell · 29th Aug 2018, 7:42 pm

What are the exact markings on that IC?

Are you sure it's an op-amp? The 1k pull-up resistor on the output suggests to me an open-collector output and that the device is more likely to be a voltage comparator. An LM311 or half an LM393 might be suitable replacements.

ianm · 29th Aug 2018, 7:49 pm

Quote:

Originally Posted by TonyDuell

Are you sure it's an op-amp?

Hi Tony. That's a good point, as I was simply going from the circuit diagram where it says "Op amp similar 741". It'll be a day or two before I actually get my hands on the board, so will report back with whatever part number I find. Thanks.

ronbryan · 29th Aug 2018, 7:57 pm

Some hysteresis (positive feedback) should be designed in to ensure clean switching around the changeover point.

Ron

ian_rodger · 29th Aug 2018, 8:02 pm

Couldn't you just replace the sensor with a slotted optoswitch e.g RS 127-3085? I have a couple of the older RS 304-560 (obsolete) to hand you could have that might do. You would probably just need a pull up resistor on the output (unless you need to invert the signal).

ian_rodger · 29th Aug 2018, 8:09 pm

Just checked, it already has an internal pull up - see attached.

Refugee · 29th Aug 2018, 11:16 pm

That last circuit is a modern one with the functionality of the OP amp built in.
What is it driving?
At worst you will need an extra transistor that can be hung between the pins with the sensor mounted on any bit of flat plastic.
If the extra transistor was an SMPSU type MOSFET you could drive a paper punch solenoid coil directly.

Diabolical Artificer · 30th Aug 2018, 6:06 am

Printers use those sensors, might have one in the shed you can play with.

Andy.

Refugee · 30th Aug 2018, 11:49 am

Andy is right about printers.
There is usually at least one in each duff ink jet printer you find and there is no shortage of those.

29th Aug 2018, 7:32 pm	#1
ianm Hexode Join Date: Jul 2004 Location: Rickmansworth, Hertfordshire, UK. Posts: 341	Opto interrupter circuit re-design - advice sought This is related to my earlier thread entitled "Driver board for piano roll perforator machine", in the Modern Technology section. Aside of a general requirement to bring the machine's circuitry up to date, there is an immediate requirement to replace an opto interrupter board that has snapped in two. A repair has been attempted by my friend who owns it, without success, so I'm looking to build a new board from scratch. It doesn't justify a custom PCB, so I would just use Vero board and arrange the components appropriately. It's a basic circuit, but two main components are obsolete, so I'm looking to use some up-to-date replacements and to alter the circuit to suit. However, although I've constructed many circuits over the years, I don't really have any design capability, hence I am seeking guidance on how to proceed. Attached is a circuit diagram. The component that I'm very unlikely to find is the op-amp and I'm thinking that perhaps a 741 might be a viable alternative. The P507A sensor is obsolete too, but I suspect that this would be much easier to substitute than the op-amp. A data sheet is readily available for the sensor, from the Toshiba website. Any assistance much appreciated. Attached Thumbnails __________________ Regards Ian McLaughlin, BVWS member

29th Aug 2018, 7:42 pm	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,224	Re: Opto interrupter circuit re-design - advice sought What are the exact markings on that IC? Are you sure it's an op-amp? The 1k pull-up resistor on the output suggests to me an open-collector output and that the device is more likely to be a voltage comparator. An LM311 or half an LM393 might be suitable replacements.

29th Aug 2018, 7:57 pm	#4
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Opto interrupter circuit re-design - advice sought Some hysteresis (positive feedback) should be designed in to ensure clean switching around the changeover point. Ron

29th Aug 2018, 8:02 pm	#5
ian_rodger Pentode Join Date: Jan 2015 Location: Greenock, Inverclyde, UK. Posts: 161	Re: Opto interrupter circuit re-design - advice sought Couldn't you just replace the sensor with a slotted optoswitch e.g RS 127-3085? I have a couple of the older RS 304-560 (obsolete) to hand you could have that might do. You would probably just need a pull up resistor on the output (unless you need to invert the signal).

29th Aug 2018, 8:09 pm	#6
ian_rodger Pentode Join Date: Jan 2015 Location: Greenock, Inverclyde, UK. Posts: 161	Re: Opto interrupter circuit re-design - advice sought Just checked, it already has an internal pull up - see attached. Attached Thumbnails

29th Aug 2018, 11:16 pm	#7
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Opto interrupter circuit re-design - advice sought That last circuit is a modern one with the functionality of the OP amp built in. What is it driving? At worst you will need an extra transistor that can be hung between the pins with the sensor mounted on any bit of flat plastic. If the extra transistor was an SMPSU type MOSFET you could drive a paper punch solenoid coil directly.

30th Aug 2018, 6:06 am	#8
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,670	Re: Opto interrupter circuit re-design - advice sought Printers use those sensors, might have one in the shed you can play with. Andy. __________________ Curiosity hasn't killed this cat...so far.

30th Aug 2018, 11:49 am	#9
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Opto interrupter circuit re-design - advice sought Andy is right about printers. There is usually at least one in each duff ink jet printer you find and there is no shortage of those.