Simple power on delay for 3.4v-5v serial device being powered by 5volt VCC

A good solution is to use a proper supervisor circuit that will provide a bulletproof reset pulse regardless of startup conditions. During the 1second delay, nRESET (usually it's active-low) will be asserted.

For example, the MIC803 series from Microchip is available with a 1.12s minimum delay time and suitable voltage settings for 5V and other supply rails such as 3.3V.

You could use such a circuit (in conjunction with a high-side switch) to control the power to the device, but it's usually better to allow the power to come up but hold the device in reset for the duration.

Failing any of those, something like this might work:

^{simulate this circuit – Schematic created using CircuitLab}

Open it and simulate it. Should get results like this:

An alternative could be something like this, but it might be a lot more finnicky. The SCR used is not ideal for this purpose and the model may be only so-so quality, so definitely experiment for best results:

A common method of achieving this would be to use a R-C network on the reset pin of the serial device. On power up this will hold the device in reset until the capacitor charges up (or discharges depending on reset polarity). The exact values of R and C can not be determined without knowing the specification of the reset threshold but will be in the range of 20K 100uF.