assist with switching
Hi audio guru, well as to your question, we know but mainly the theoreticals at least for me as a student we hardly practicalise and u have to admit there is a diference between the two.
I need your help plz. I have made the siren circuit but I used discrete 555 timers bcos I could not find the um3561 ic. But I have a problem with the switching again, this is bcos with this circuit the first timer acts as a modulator with three selectable resistances between pin 7s resistor and pins 2 ad 6 on a common line, each resistor corresponding to “high low”, “wail” and “yelp” sounds.All these discharge through a capacitor to earth. The ouput pin 3 is connected to a fixed resistor which is in series with two capacitors in parallel for wave shaping. These capacitors are to be brought into circuit ie earthed for only the last two sounds, ant then a commom lie between all three is conected to the control of the second timer timer. Now using the the three outputs from the counters I connected C1815 transistors for switching. For the h-lo it requires no wave shaping so its switches fine, but for the next two sounds I need to switch both the resistor and the wave shaping capacitor but I noticed that the transistor I connect to earth ie its emitter to earth while its collector is to the wave shaping capacitors makes the whole circuit go haywire. The whole switching sequences seizes. I first ganged them that is in twos for the wail and yelp their bases but no way. I separated them no way. Plz hw can I switch both the selected resistor and the gorunded capacitor simultaneously with transistors at the same time. I need a practical solution bcos now the outputs I get do not produce realistic sounds. I read a book and I discovered that using emitter resistors might work but I feel this could affect the time constants of the RCs is this correct? And what values do I use?. As for mosfets I can find no low voltage ones here the best I could find where 2, 50volts ones and this is a 15volts cct.So u see I need to use this xsistors but what is the solution? Thanks