The optocouplers in the dmm are reportedly TLV817B. The emitter resistor on the output npn is shown on the schematic to be 1.5K. I measured it to be 7.35K. The input resistor in series with the LED is listed as 3.3K. I have not opened the dmm to see if the schematic is accurate. I agree that these should not matter. I will get to the sigrok functioning later today or tomorrow.
On Thu, Dec 14, 2017 at 10:00 AM, Galen Seitz <[email protected]> wrote: > On 12/13/17 23:03, Russell Senior wrote: > > The precise levels are not supposed to make a difference. Below a > > negative threshold and above a positive threshold should be enough. > > From memory, original RS232 was +/- 12V, but any remotely modern PC > > would use +/- 5V-ish. > > And the reality is that in most cases a simple unipolar TTL signal will > work. RS232 receivers usually have the logic threshold near +1.4V, plus > or minus some hysteresis. For example, the TI MAX232 has a typical > positive-going threshold of +1.7V, and a negative-going threshold of > +1.2V. Another older example is the OnSemi MC1489A quad RS232 receiver. > The typical thresholds for this device are +1.95V and +0.8V. > > galen > -- > Galen Seitz > [email protected] > _______________________________________________ > PLUG mailing list > [email protected] > http://lists.pdxlinux.org/mailman/listinfo/plug > _______________________________________________ PLUG mailing list [email protected] http://lists.pdxlinux.org/mailman/listinfo/plug
