Summary

This is a remixed version of david crockers differential infrared z probe.
I uploaded the eagle source files, so you can change what ever you like.
I also added the gerber files as a zip file, which i sent to elecrow for manufacturing the pcb (they are super cheap, a buck for a pcb two sided. if you want to order this pcb from elecrow, please use my referral link: http://www.elecrow.com/referral-program/MTgxNjBqMnQ=/ )

I changed the smd ir diodes for regular ones, as you can get them dead cheap. additionally i mount them in a shroud, so they are positioned properly and the wider opening angle does not matter. I also exchanged the big capacitor, with a ceramic smd one.

The pcb is not compatible to the crocker ir board regarding dimensions, so i designed a custom mount for it, but i don't have an e3dv6 mount or anything like that, since i am using a replicator.

BOM:
1 x smd Resistor 3.3kohm 1206
2 x smd Resistor 3kohm 1206
1 x smd Resistor 1kohm 1206
1 x smd Resistor 866ohm 1206
1 x smd Resistor 330ohm 1206
1 x smd capacitor 22uF 1206
1 x smd capacitor 100nF 1206
1 x smd capacitor 1nF 1206
1 x smd inductance 1uH 1206
1 x smd led red 1206
1 x Attiny25-20su
2 x Infrared LED (SFH4550 better a 3mm ir diode you can get them on aliexpress in pairs with photodiodes in a bag of 100)
1x photodiode (the original spec uses a phototransistor, just add a transistor, to the diode if necessary)
1x pcb (have it manufactured at elecrow, or mill it yourself)

Notes:
The photo diode in the schematic has to be reversed, also the printed + and - symbols on the pcb have to be reversed.

The sfh4550 ir diodes have a small opening angle, but you can use any cheap ir diode with the shroud. The shroud only fits 3mm diodes, if you are using the sfh4550, you have to change it.

Angles of the diodes are 56 and 45 degree, as calculated to provide best precision. Trigger height is 4mm

Sorry no images of the printed part.
firmware for programming the attiny is available here:
https://github.com/dc42/OrmerodSensorBoard/tree/master/Firmware/Mini-differential-IR/V1.2

Big thanks to david crocker, for the omerod design.
https://miscsolutions.wordpress.com/mini-height-sensor-board/

PS: you might want to change the 1206 parts for smaller ones, so you can make the pcb smaller, to match the crocker board dimensions.