5 replies to this topic

[Ember]

Could this type of component be useful for the construction of timing systems?

CdS Photo conductive cell

Available in packs of 50 from ebay here

[oldslot]

Ember, on May 19 2010, 10:23 PM, said:

Could this type of component be useful for the construction of timing systems?

CdS Photo conductive cell

Available in packs of 50 from ebay here

yes Em thats what I am using on my track as far as I know, well they look the same. I use a small flouro tube over the sensors for the light source they work through a couple of afx counters Joe Z set it up for me as I am not very electronically embellished.

[kalbfellp]

They are LDR's we used them back in the late '60's for lap counting,I have also used them for web detection on printing press, BUT are a little large in diameter and really need an amplifier circuit for good reliable detection.
Pretty sure I had then just controlling the base of a transistor to then switch a relay.

This was all before thing called computers!

Edited by kalbfellp, 20 May 2010 - 12:23 AM.

[SlotsNZ]

I'd be a bit suspicious that the rise and fall rate may be slow enough to cause cars to get over them and gone again before sufficient state change occurred to trigger a resistance change within a detectable band.

Also, with the stated resistance range of the ones shown, you couldn't just use them by themselves like an off / on switch. The minimum resistance stated looks to be too high to be within switching range for most old parallel ports. I think they may need to be part of a circuit...... but

- But I'm no tech. someone with the right letters after their name may well correct me.......

BTW, while I think of it since it has to do with timing.
UR3.0 can now receive commands (interrupts for timing) via simulated joystick via USB port, so can Race Manager X from USA.
Won't work with LT 2000 unfortunately, I haven't thought about SRM2.5.

I have a couple of Joystick to USB adaptors coming to test, which appear to use the built in HID command set with windows which would allow people to plug in an RS232 plug to the unit, and plug the output cable into the USB port of any modern PC.
Both the timing programs allow for choosing each "Button number" for each lane.If it works, it will give a cheap, long term solution for free timing software packages into modern PCs which don't have a DB35 or RS232 port.
I just have to suss out all the pin number assignments without cooking the test units - which are sealed......grrrrrr

- They're a nice cheap unit that won't break the bank. More in a couple of weeks.

[Ember]

Just saw them and wondered about the possibility seeing as the holy grail z1951s are getting precious.

[Holty]

As Phil said they are light dependent resistors.
I've used 2 similar devices on my track but had to build a circuit with transistors to NOT the signal (because their resistance is high when you want it low). The circuit was based on one here on the forum somewhere, I think Phil from Tassie may have posted the link to the diagram.
I had to incorporate some variable resistors to control the base current to get them to switch with the right sensitivity.

I found the sensitivity OK in the middle of a short straight about 1.2 metres long. I've got them hooked up with an old calculator (short the [equals] contacts and push zero plus one before race start) and an old digital timer (shorts the [set minute] contacts).
Another alternative I tried was hooking the switch circuit to parallel ports and software and it works ok there as well.
I have found longevity issues with them though. Their surfaces may be a bit sensitive to the conditions in my shed and I've replace each sensor once over 3 years.

Holty