Whats inside an OMRON E3JK - R4M1 Infra Red Beam Sensor - Page 1
Forum section: electronics / projects

author: Satbeginner
author_rank: Regular Contributor
timestamp: March 29, 2020, 02:42:22 pm
content: Hi all,being in Spain where we have an almost complete lockdown, I found time to fix my intermittent IR Safety Beam at our gate.Usually it works OK, but when it rains, or on colder days because of condensation, drops on the reflector or on the device itself will prevent our gate to close.The thing is, the IR Beam security is only active when the gate is closing, makes sense, doesn't it?Because that's when you can get caught trapped.So the gate will open, but will refuse to close again....Again, me being the optimist, these devices are supposed to be OK to a maximum distance of 4mtr, but from left to right our gate is close to 5 mtr...., so who is to blame??I have one of these cheap Chinese "OMRON" E3JK-R4M1 sensors installed.(Not sure if these are the real OMRON deal, or just really good imitations)!! Carefull!! These devices exist in various types, mine if is a 12-24VAC / VDC version,notthe 240VAC version!!This is an active IR Transmitter / Receiver in one little box, with a Retroflector at the other end.A science teacher many moons ago emphasized on the difference between a Reflector and a Retroflector:A reflector is like a mirror, angle of entrance is angle of exit, so you can go actually around a corner using a reflector, like a periscope if you use two.A Retroflector does reflect a beam of light in the exact same direction as where it was coming from, because it has series of 90 degrees inverted pyramids on its surface.Anyway, since mine ís working OK when there was no rain, and it would work also when I would wipe dry the retroflector when wet, I thought to myself: "Can I increase the sensitivity a bit?"The answer to this question could only be given when I knew what was inside the little box, so that is what I was going to find out.Basically they "mis-used / abused" a CMOS 4013, a DUAL D-Type FlipFlop.One FlipFlop was used as an oscillator, to transmit a continuous stream of short IR pulses.The other FlipFlop was used to check if the received pulses were time-related to the Transmitted pulses, so they would check the level of the IR pulses received, exactly in sync with the transmitted pulses.To do this, the trailing edge of the short pulse from the oscillator used to transmit the IR pulses, is also used to clock the second FlipFlop.Furthermore, the received pulses are AC coupled to the second FlipFlop, so using a torch or other lightsource will not disturb the actual function.Another -quick-and-dirty- solution is, they used the D-input of the second FlipFlop as a sort of comparator to distinguish between "Yes" there is a pulse, or "No" there is no pulse.Attached I will put a picture of what's inside this device and the diagram I deducted from the inside of my device.To increase the sensitivity I added a 1 kOhm resistor in parallel with the 330 Ohm current limiting resistor used to determine the current through the IR transmitter LED.By doing this, the current in the IR LED went up from 19mA to 25mA, but at a Dutycycle of only 0.7% I think that will not be a problem for the transmitting LED.So, technically I did not increase receiving sensitivity, but I increased the overall sensitivity by transmitting at a slightly higher level.Un saludo from Spain, stay safe, stay healthy, stay indoors,LeoModified for small typo's