| ??? 01/21/05 16:17 Read: times |
#85520 - Threshold level Responding to: ???'s previous message |
Michael said:
However I always add an additional 1N4148 type silicon diode in series with the transistor base to easily raise the switching threshold to two Vbe drops above ground. This solves the problem I have seen countless times where the driver from some non-compliant RS232 equipment is using a GND reference for its TxD pin. Another remedy would be to add a resistor in parallel to base emitter junction. If this shows the same value as the input series resistor, then threshold voltage is shifted up to about 1.4V. This additional resistor would also solve the problem of increasing input impedance, when transistor or protection diode aren't forward biased. These both resistors should be decreased somewhat, because lower impedances give better performance, something about 2k7 for each is a good idea. By changing the ratio of both resistors the threshold can even be furtherly adjusted. Kai |
| Topic | Author | Date |
| Instead of MAX232 | 01/01/70 00:00 | |
| Dont do this. | 01/01/70 00:00 | |
| I've seen worse! | 01/01/70 00:00 | |
| Hysterisis lacking | 01/01/70 00:00 | |
| pin connectors | 01/01/70 00:00 | |
| The Specs | 01/01/70 00:00 | |
| Check this Kuan | 01/01/70 00:00 | |
| Male/Female? Pin Numbers? - DTE or DCE? | 01/01/70 00:00 | |
| Previous experience | 01/01/70 00:00 | |
| OH NO! NOT AGAIN | 01/01/70 00:00 | |
| Receive-Only | 01/01/70 00:00 | |
| Let's analyse: Why is it wrong? | 01/01/70 00:00 | |
| Why all this excitement? | 01/01/70 00:00 | |
| that's the TTL side | 01/01/70 00:00 | |
| No! | 01/01/70 00:00 | |
| ah-ha! | 01/01/70 00:00 | |
| Then I apologize... | 01/01/70 00:00 | |
| did you mean this | 01/01/70 00:00 | |
| RS232 Bus Input Lines of Receiver | 01/01/70 00:00 | |
| Threshold level | 01/01/70 00:00 | |
| Resistors work too | 01/01/70 00:00 | |
| Rf makes Schmitt-trigger performance | 01/01/70 00:00 | |
| Works for some applications | 01/01/70 00:00 | |
| link, please | 01/01/70 00:00 | |
| found it | 01/01/70 00:00 | |
oh tresting again | 01/01/70 00:00 |