I'm under way with my development circuit featuring G8GKQ's transistor changeover switch from the Beginner Question - Complete System thread and Ian Waters' sequencer from the Wiki. See picture. The jumper is in and the test slide switch takes the place of Portsdown Band selection PTT.
I've learnt that turning it on means pulling the J2E terminals to ground and that both 1K resistors in the sequencer are important to making the switch work. So on second attempt, after consulting the analogue electronics engineer at the other end of the office, I've wired it correctly.
Snag pins 3 and 10 remain fast a 0V so no relay action. 12.2VDC supply
I measured IC pin 2 changes from 1.02 to 6.62 V while pin 9 goes 5.8 to 2.02 and vice versa. Pin 1 changes 0.5 - 3.3 V and pin 8 changes 1.02 - 2.9V therefore the RC part is working.
I guess the transistor bias is not sufficient to reach the high threshold voltage of the AND gate? Any ideas? What voltage values did you consider in your design Dave? In case I've a hidden fault in my work. It's partially working which is a crumb of comfort.
There are two unused gates on that device and I would like a 3 band Portsdown with sequencing .....
- 20171101_G8ADE sequencer development.jpg (487.96 KiB) Viewed 310 times
I was aiming that the voltage swing should be from 0 to about 10.5v. Calculation for the high voltage is (12-Vce sat)*1000/(1000+100). Vce sat should be about 0.4V.
With the switch input grounded, please check the voltages on the base, emitter and collector of the first transistor. Base should be about 11.3v , emitter 12v and collector 11.6v.
On my breadboard I've redone the circuit with 2N3906 transistors and added the 1K resistors off the sequencer from the 100R resistor to connect to ground. Voltages at tx 100R are 11.03 / 1.03V and at rx 100r are 0.0004 / 11.1 V. That would work permanently if I moved those 1K resistors to the respective transistor circuit?
I think that you had wired the BC214s incorrectly, as the emitter should be at 12V, the base 11.3V and the collector 11.6V.
The indications with the 2N3906s are correct, so you should connect those up and it should work.
Andy Britton my colleague at work had sketched in the 1K pull up resistors mentioned above and today I noticed there were diodes after these.
This works very well
Although the LEDs stay on together for 4 seconds the scope trace comparing pins 3 and 10 of the IC looks like this:-
Both off / changeover time is c. 2.3 seconds at present. I think I'll change the 47K resistor for RC timing to a trim pot.
I'll re-measure at the relays when I've mounted them in a better place.
To-do next is make a fair version on one board or two stacked QRP-Labs style. I wonder if I can use the other 2 gates for other pre-amp power and relay signals running on the same switch interval? Then work out what to do to make a Portsdown 3 band system.
I think I'll make my 70cm DK7ZB beam tomorrow while it's raining. B&Q materials plus John GM8OTI's SOTA friendly construction techniques.
It was drawn in TinyCAD.
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