Hi all,I bought a KE72 for my cockpit project. In their web site they state:"In addition to "dry" contact closures, connection to 5V CMOS or TTL circuits is also possible. The KE72 considers a low level as an active input."Does anybody know how to do this? I already have a TTL circuit with its own 5V power supply. I asked Hagstrom how to do that but they never replied.Thanks,Gabriel

Gabriel,The information on the Hagstrom Electronics web site indicates that each of the encoder's inputs is separate and is activated by a "low" level. Generally this low level is generated by a switch which is connected between the input and ground. Based on the information on the site, it appears to me that all you need to do is connect a TTL or CMOS output to an encoder input. The TTL or CMOS circuitry will have to share the same electrical ground as the encoder. Effectively, the logic output is acting as an electronic switch inplace of the mechanical switch.One bit of information I did not pick up from the site was how long the signal into the encoder's input has to remain active to be picked up. I would expect something on the order of 100 milliseconds should do it.What sort of circuit are you planning on using?Mikewww.mikesflightdeck.com

Thanks MikeI also think that the circuit's ground has to be connected to the KE72 ground, although connecting an externally powered circuit to the KE72 scares me a bit, I must confess.Right now, I have a simple TTL circuit that I can use just to test doing this with the KE72, but in the end, the circuit I want to connect is to read the input of rotary encoders. It'll be based on the LS7083 from USDigital.Gabriel

Gabriel,Connecting an externally powered circuit to the encoder should not be a problem as long as the external power source has a ground that really is ground. It really is no different than plugging an externally powered set of speakers into your sound card. I suppose it's possible that some older or perhaps defective power modules might cause some grief, but I have not run across anything like that since the days of vacuum tube televisions. You can check for this problem by using a voltmeter to measure the voltage difference between the encoder ground and your external power source ground (with the external power source plugged into AC and powered up). Depending upon the voltmeter, you will likely see several volts AC. (If you see 120VAC, go no further. You have serious problems.) If you place a resistor on the order of, say, 10 kOhms across the meter input while make this measurement, the reading should drop to almost nothing. If you get readings greater than a volt or two with the resitor in place, you've got rather more leakage in the power source than I would be comfortable with, and another power supply would be a good idea.The LS7083 is a neat chip. You may run into problems getting reliable operation with the KE72, however. Let me say up front that I have not used this chip or the KE72, and may be totally wrong. Nonetheless, let me lay out my logic so if you do see flakey results you will perhaps have at least one possible problem to check.Mechanical switches don't close instantaneously. They bounce. You can't see it, but electronic circuits very definitely do. "De-bouncing" logic is commonly used to get around this problem. Sometimes the logic is implemented in hardware, in other cases (like keyboards) it's handled in firmware. Without de-bouncing, what the user intended to be a single switch closure may be interpreted by the circuit it feeds as a sequence of pulses followed by a switch closure. The de-bouncing process can take a few milliseconds, depending upon the switch.Here's the possible issue: If the KE72 uses switch debouncing, as I would expect it to, the LS7083 may not output a pulse of suitable width to avoid getting ignored by the de-bouncing. It appears that the longest pulse the LS7083 produces is on the order of 25 usec, which is perhaps still shorter than the de-bounce window.If this occurs a possible fix is to follow the LS7083 with a monostable to stretch the pulse a bit.Mikewww.mikesflightdeck.com

Thank you very much Mike, specially for the info about de-bouncing.Gabriel