Fullscreen HTML5Med Res (??MB)HTML4

recommend a replacement? (F. C., Maroubra, NSW) ● That is a common style of relay made by many manufacturers. We believe that Altronics S4199, which is currently available, is virtually identical. Jaycar’s SY4051 is similar but rated at 10A. That should be sufficient, given that it isn’t switching the full load current (the parallel thermistor carries some). There’s also element14 4228168, which looks to be compatible, although it is 5mm taller and doesn’t have the NC pin (which is not used in that project). We think it will still fit in the box despite the extra height. Advertising Index Altronics.................................29-32 Beware! The Loop......................... 8 Blackmagic Design....................... 7 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Emona & RIGOL Contest.............. 9 Emona Instruments.................. IBC Jaycar............................. IFC, 55-58 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 OurPCB Australia.......................... 5 PCBWay....................................... 11 PMD Way................................... 111 SC Advanced Test Tweezers...... 53 Silicon Chip 500W Amp............ 93 Silicon Chip PDFs on USB......... 37 Silicon Chip Shop.................86-87 Silicon Chip Songbird................ 26 Silicon Chip Subscriptions........ 13 The Loudspeaker Kit.com.......... 10 Wagner Electronics..................... 12 Next Issue: the January 2025 issue is due on sale in newsagents by Monday, December 30th. Expect postal delivery of subscription copies in Australia between December 30th and January 13th. 112 Silicon Chip Improvements to Relay Selector circuit I’m an avid reader of Silicon Chip! Recently, I came across the Pushbutton Relay Selector circuit in the Circuit Notebook section of the January 2006 issue (siliconchip.au/Article/2537). Looking at the circuit and reading the text, the basic principle is the 4017 counter/decoder counts up and sequentially brings O1 through O9 high. It does that until it connects with the switch being pressed, which then stops the clock from being fed to CP0. I think there is a problem since each of these are sequentially cycled through. For example, pressing S5, before Q4 is fed a +5V signal, Q1 through Q3 will have been fed that voltage as well in sequence. It just will not have been routed to IC1c to stop the clock pulses. This means if any except the first button connected to O1 is pressed, all before it in sequence will be pulsed before settling on the pressed channel. If these are big relays, that will make quite a bit of chatter, but more significantly it will turn on potentially unintended channels, as would be the case in my application where line-level sources are to be selected. I have a fix for it in my application, which could be adapted to the author’s application as well. I am using latching relays and the driver IC has an ENABLE pin. This can be connected through a 4069 inverter to pin 10 of IC1c to disable the relays until the clock stops, at which point only one will be activated. A similar action can be achieved in the author’s example by connecting the positive end of all the relays to the collector of a power Darlington PNP like a TIP107. Its emitter would be tied to +12V, then its fed base via a 10kW resistor by pin 10 of IC1c. When that pin goes low after a selection is made and the clock stops, all relays are enabled. The approach used in this circuit is elegant and achieves many of the unique attributes of an interlocked mechanical push-button array at a much lower cost. Is there a reason this was not considered with the original circuit? (H. H., Chapel Hill, North Carolina, USA.) ● Your suggestions are certainly interesting variations on that circuit. We think the reason that they were not incorporated in the original circuit is Australia's electronics magazine that it probably cycles too fast for the relays to actuate. It looks like the cycle frequency is around 20kHz. That means each transistor will be on for around 50μs. A relay normally needs several milliseconds to actuate. Consider that the circuit uses small Mosfets to switch the relay coils with 100W series gate resistors. The resistors and gate capacitances (around 60pF each) will form a low-pass filter with a time constant of 6ns. By increasing the resistance and/ or adding capacitors from each gate to ground, you can increase the time constant enough that the Mosfets can’t switch on while the 4017 is cycling. It would have to stop to provide a long enough pulse to switch the Mosfet on. Increasing the resistors to 10kW and adding 100nF capacitors from the gates to ground will give a time constant of 1ms, which is far longer than the 50μs on-time during cycling, but short enough not to notice when you are purposefully activating a relay. Sourcing or substituting OPA2134PA op amps I’m trying to find a replacement for the OPA2134PA op amp that was used in the Studio Series Stereo Preamplifier design (October 2005; siliconchip. au/Article/3203). I have built the preamp but am unable to source the op amps. I am going to use it as a replacement for the Series 5000 preamp (still working) when it finally dies. Any suggestions would be appreciated. (V. P., McLoughlins Beach, Vic) ● OPA2134PA ICs are still available from multiple online retailers, and they appear to still be current devices. For example: • RS 285-8069 • DigiKey OPA2134PA-ND • Mouser 595-OPA2134PA There is another variant available, the OPA2134PAG4, which is essentially identical. We can’t think of any reason you couldn’t use NE5532s or LM833s instead, as we did in later designs with similar circuits. They have similar if not superior performance (eg, slightly lower noise). The main difference is that the OPA2134 is a FET-input op amp, which is important in some applications, but it won’t make much difference in the Studio Series Preamp. SC siliconchip.com.au