Hello.
As part of a project, I have been creating an electronic circuit designed to monitor temperature and output various indicators dependant upon the temperature measured by the temperature monitoring device. I have uploaded an attachment with this post showing the part of the circuit I am having trouble with.
You'll have to excuse the tidyness of the circuit. It is still in it's draft form and will be remade once I can confirm that it works as I intend it to. It is built using a piece of software called 'Livewire'. Bare in mind that this is an amateur circuit and will be built but only for the purposes of the project and will not be used to actually monitor temperature.
The first problem I have is located in the yellow box. From my understanding of SR Flip-Flops, whilst both of the inputs are high, the output will be low. If the latch is set where S is active low, the output will then be high and stay high regardless of S, until R becomes low to reset the latch. The problem I am having is when I test the circuit the initial state of the output of the latch seems to be random, but works correctly. I just wondered if either the circuit was set up incorrectly, or if this is a problem that is restricted to livewire, and will not be replicated in the real circuit?
The second problem I have is located in the white box. I am using two 4026B chips and an astable to count for how long the temperature is raised above a certain level. After 20 seconds, the latch should be set, but will reset if the temperature then returns to a satisfactory level. I've tried to accomplish this a couple of different ways, but none so far have worked. The image shows my latest attempt. Because I'm using these particular chips, I don't have access to the binary input to the 7-segment displays. Therefore I have attempted to make do by making the latch set when segment F on the left hand side 7-segment is a one, as this should be the first time when the segment lights. The problem with this one however, is that when the latch is reset, the counters are reset at the same time which seems to cause all the segments to light, and sending a one to the output, which is unintended. Note: I had to use the transistor as a not gate because a not gate doesn't correctly pick up the input voltage, presumably due to the number of gates the signal has to travel through to get to that gate. I believe I will able to use a not gate when building the circuit.
If anybody has any thoughts, I would much appreciate it. Thank you in advance!