 great search brought to you by Digikey and eight of your things Digikey. Every single week lady had used her power of engineering to find the things that you were looking for and the things that we were looking for during this chip shortage. They needed a what is the great search this week. Okay this week's great search as you very intelligently foretold is related to part shortages. We're in a chip shortage which means that not only are there current parts that are hard to get but older parts that we've been using for a very long time decade plus have been harder to get because companies are focusing on the more profitable product with their newer ones and so very popular things that we thought we'd be able to get for a long time are now not recommended for new design discontinued end of life. So the part that we're gonna be looking at today is the APX803 which is the part we've been using for like again over a decade. It's a power-on-reset circuit chip which we use to generate reset pulses as our power supplies come up from ground to you know 3.3 or 5 volts. So let's look at the computer I'll show you where I use this part and how. So this is an example the APX803 SAG. Yeah at the time this was just the least expensive easiest to use power-on-reset circuit that I can get from Digi-Key. It comes in three pin SOT23 it looks at the VIN line and when this when this pin you know gets up to a certain voltage in this case I think 2.6 volts it will start a reset pulse on the TFT reset pin which will pulse down hold it for you know about 200 milliseconds and then release and what that does is if you have you just especially displays I found TFTs and OLEDs you know sensors I squared C sensors you don't mind that you know the power comes up slowly they'll do their own little power-on reset or you can send them an I squared C command but we've noticed that TFTs and OLEDs really they can boot up in a very weird state they really want a fresh reset pulse right out of power on and normally you can just use a microcontroller pins you have a lot of pins connect one of those GPIOs to the reset then before you initialize the display you toggle the reset and you're you've got a clean set of registers to go on but sometimes you don't have a lot of GPIO pins you know in Arduino you might not only have like a dozen pins you really want to save them especially if you're only going to use that pin once at the very beginning of power-on so that's where a circuit like this comes in this little chip will just hold that reset in line low for you keep it nice and clean and then release when the power has stabilized but as I mentioned this part is not recommended for new designs anymore this is the sorry this is the datasheet NRND they recommend the APX 803S which is also not available one thing to watch out for is this chip has two versions the SA and the SR whether pin 1 is ground or reset basically makes a difference we want pin 1 to be ground and then reset and power not one you know reset ground and power of the opposite way because we want something that we can drop into our existing designs I mean if I had to I could reroute the PCBs but boy I really don't want to do that because I've got like 20 designs that use this sensor this supervisor so let's see what we've got you know again we used to pay about nine cents for these we still have some on order but don't know when we're gonna get them because it's last time by so let's get something similar if we want something that's a simple reset power on reset circuit with one voltage monitoring I do want open drain or open collector because oftentimes I will be monitoring the V in the power inputs and then but not necessarily a three volt line the three volt line you know may have a little bit more jitter in it that said once you get to like about 2.6 plus volts the 3.3 volt power supply will start to kick in I mean it's it's gonna be lower because of the dropout but it will be slowly coming up I can hold that reset line until it gets to 3.3 volts well within a hundred millivolts milliseconds and then release to put the TFT in a good state and we do want it into that sought 23 for an active low reset for the reset timeout I don't really care even this one is about 140 to 200 milliseconds I'm flexible also the voltage threshold I'm flexible so let's view similar so first up I want something that's active because I don't want another NRND thing so let's only look at those next up the voltage threshold this is important you don't want it to be too low because I want to make sure that we trigger when the power supply is is coming up and it's in a good state but I don't too high because remember you know the power supply is going to be going above 3.3 volts I don't want there to be like little dips if it drops 200 millivolts to 3.1 I don't want that to trigger it so 2.6 volts is what I picked before but I think something between 2.5 and 2.9 will probably be just fine that's still well below the 3.3 volts and don't forget this is also I'm monitoring V in not the 3.3 volt line and so you know I have a little bit more leeway there okay so let's apply all let's also look only at what's in stock because I have to purchase these now to tide me over until I get the the order that I booked a while ago and second let's sort by pricing because I need to buy about 10,000 of these so looks like we have a couple options here there is of course the APX 803 L20 so that's very promising I think this is just you know the new version again we want pin 1 to be ground so let's make sure pin 1 ground yes we want the slot 23 version not ours let's look at the part number and make sure we get the right version and hold on they usually have a part code okay so I want let's see this is the APX 803 L20 and then is it SR no this is SA this is the correct type so this looks like it's got the right pinout it's the SA pinout and then let's see 803 blank 0 milliseconds voltage SA package and then the real active low open drinks this is actually pretty good and oh three oh sorry 20 the L20 means it's 220 milliseconds which is exactly the same thing as we had before so this is a great option so I'll probably pick up some of these but I also want to look at some other options so looking at the RT 9818 looks like there's these are available in slightly lower voltages so 2.7 if I wanted something closer to my original spec maybe you're a little pickier on that so for this one okay again you have to be careful because there's so many package options this is 91 9818 C and C is also 220 milliseconds good reset bar active low good dash 2.7 or 2.9 so that's good 2.7 to 2.9 volts these are both lead free and then GV G is green halogen free and then V so it's the SOC 233 not L type so let's look at SOC 23 there's two SOC 23 options again there's L type and not L type the one that's available is this one which is reset ground VDD let's look at this reset ground VDD which is actually not we want that's the opposite orientation we want ground reset VCC so we can't use these two and then let's look at one more option here the TLV 803 EA 26 also nice the voltage is much closer again it's all about trade-offs the voltage here is going to be 2.6 volts you can tell by that 26 but let's also make sure that this is the right pinout so we get this data sheet takes a moment okay scrolling down okay so again so many options TLV 803 and the two versions are 803 E yeah 803 EA 803 EB 803 E is open drain active low good B is 40 microseconds that's very little sorry E yeah a sorry a is 200 milliseconds which is what we want B is 40 microseconds much too low so we'd go with the A version this one then 26 which means the threshold voltage is 2.6 volts and then our DBZ R so R means pin 1 is reset pin 2 is ground which is again the wrong package so you can't use these either so you know it's interesting it's like there are a lot of options and unfortunately once we get past here that the pricing it's a little expensive but so far you know the trade-off is is that looking at the ones that have the closer voltage 2.6 2.7 not gonna work because the pinout is wrong so alternative is one I can use this version with the higher voltage I think it's gonna be okay I think 2.9 volts is not too close to the 3.3 volt logic level hopefully it doesn't dip I mean that's like 0.5 volts difference so hopefully it won't dip too low and if it does it'll auto reset I don't know maybe after testing I'll determine if I need to add more capacitance on the power line but it is the right pinout and there's 23,000 in stock so I think I'm gonna go with this again test it out make sure it works on all my designs if it doesn't and I have to go with the 2.6 volt voltage reading I'm gonna have to swap those two wires the stencil will be the same but I'll have to make sure they don't get the wrong part with the the wrong PCB version which is a little frightened to me so I'm hoping that this version works I'm gonna pick up some of these hand solder them into my TFT designs and then just test them with a couple like flaky power supplies and see what occurs and hopefully these can tie me over till my order comes in that's the research