As I wrote, people just don't want to hear it. E.g. a low-end micro is in the 0.50 USD range in quantity. So much for
The cheapest MCU is still more expensive than a single 555 or logic IC, even when external components are accounted for.
I've heard that many times before but never seen any evidence that MCUs are really cheaper, care to post some links?
So what the cheapest MCU might only be $0.50 in large volumes but the 555 or logic ICs are still much less when bought in the same quantities.
The cheapest MCU I can find in RS is the PIC10F204 at £0.25 each, in quantities of 100.
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=7047627The cheapest 555 is only £0.088 each, in quantities of 75.
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0785818AWhat about logic gates?
A quad NAND IC can be bought for just £0.064 in quantities of just 10, even less than the 555. I found some cheaper single gate packages but you can't make an oscillator with one gate unless it's a Schmitt trigger.
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6631887Then what about using a Schmitt trigger? Good idea (even though I do say so myself) a single Schmitt trigger IC can be bought in quantities of 50 for just £0.047
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0510352Go on tell me I'm wrong again, show me where you can buy genuine MCUs for £0.047 (just 7.44 US cents) each in quantities of 50 from? All right maybe that's not fair, a Schmitt trigger IC will require a extra resistor (or a couple of diodes in this case) so as add on 0.5p (0.8 cents) assuming you buy your resistors in 100s not 1000s or a little more for a dual diode.
Don't get me wrong, you raised some valid points regarding flexibility, oscillator stability and accuracy but cost is not one of them, sorry it's bullshit.
I like MCUs myself and are just getting into them but would never use one to just flash a couple of LEDs alternately. I'd opt for a logic IC every time, especially if it's run from a higher voltage than 5V: no need for a separate regulator and the old CD4000 series has current low outputs which are handy for directly driving LEDs: no series resistor required.
you can get yet closer to 0/100% by powering the RC circuit from output and no using the discharge pin, in this way you don't need the minimum resistor as during discharge there is no supply to protect from and it discharges through the output whilst low (totem pole output)
You mean as per my previous circuit using the 7555, so it's being used as a Schmitt trigger?
Yes, that will work very well, as long as you're aware that with the NE555 (not the CMOS versions) there's slightly more output saturation loss when sourcing (1.4V) than when sinking (<100mV) which will make the frequency and duty cycle more dependant on the power supply voltage, the load connected to pin 3 and that when the resistor is in the centre position the duty cycle will be higher 50%, especially at low supply voltages.
I'd recommend that sort of configuration for CMOS versions (TS555, TLS555 ICM7555 etc.) rather than the TTL because it doesn't suffer from and of the issues described above, as long as the output isn't loaded too much.